Here's a bunch of cool mods, that you already know for most of them :
Also : [WARNING] Wall of text. I tried to not make it compact, but it's still big.
EDIT : Fail, posting crushed all the spaces i added, actually making a giant wall of text.
EDIT 2 : Re aded manually all the spaces. Why, forum, why do you hates me so much?
EDIT 3 : Just wanted to say that with the 1.6 coming, a update will happen, so it would be a good time to throw new mods in.
UNDERGROUND BIOMES
That mod was rejected before because it's new stones and cobblestones weren't compatible with most recipes, and because the vanila stone was entierely removed from worldgen. In the recent versions (read the changelogs) vanilla stone is back in the worldgen (and is quite common), so forestry stone hives can spawn again (this was a problem), and some forge oredictionary support have ben added for all stones, cobblestones and bricks. It works in crafting recipes of most mods, and even if it don't works in a lot of machines, you can always craft the mod cobblestones in vanilla cobblestone (2x2, so you can do it without a workbench and a packager sould be able to automate it fine), solving all compatibility problems. It's a great mod as it makes mining far less boring, and add a lots of new building materials.
Now, as a worldgen mod, and a major one, we can suppose it'll lead to some mess in old worlds (sharp biome cuts), but as it's all underground, and its' just blocks replace, it won't mess the surface or caves and the cuts won't really be visible, and even by tunneling or in caves if your tunnel isn't too wide you won't notice it (now if you dig a giant room exactely on the cut place, you should see it, but that's improbable).
BIOMES O PLENTY
The problem here is that pepole wil say :
-But we already have EBXL
According to
the poll results, There is a bit more players wich prefer BOP to EBXL. Now, i won't ask to remove EBXL, it's a great mod and it has the greenest meadows ever. And removing it would break evrything. I'm asking for having EBXL and BOP together (it works. With some easy configwork, i've been able to make them fit nicely together). As BOP add a new world type with it's biomes in, adding it will cause all old worlds not generating it's biomes in, so there will be no terrain generator changes and no sharp biome cuts (understand : in those worlds, it'll be like BOP have never been added, allowing perfect forward compatibility), while for new worlds, you'll have the choice of using the BOP biomes or not, without modifying the config, so anyone wich don't like it can not use it while not uninstalling it, so not breaking lots of compatibility with servers. There is no risks at adding it as you can ignore it completely if you want.
-I can't find a specific ressource in middle of this giant amount of biomes
While EBXL have good cross-mod compatibility, it don't generate some of biome-specific ressources (emeralds, but also a few more things) in it's biomes (Stuff like Gregtech biome-based ores works fine and is even more common). Biomes o Plenty, while it used to have a awful cross-mod compatibility (you needed a separate mod wich added the necessary compatibility with most mods), have since the 1.5 updates added all that missing compatibility (again, read the chngelog. Changelogs are your friends), allowing for example thaumcraft nodes in all biomes (it was broken), and the possibility for all biome specific ressources, from mods (Gregtech ores, railcraft white stone quarries, Natura stuff, Thaumcraft trees, ...) or not (emeralds, slimes, ...) to spawn in their biomes. At the end, those biome-specific ressources are now more common that they were before. You can easily find railcraft stone quarries or Gregtech ores, or vanilla wood, even with the giant amount of new trees it adds. And it adds more flowers than EBXL (they are forestry bee-compatible BTW) allowing to get all kind of dyes while EBXL give you only a few.
This mod give a giant amount of new blocks (mostly wood, but also some stones, bricks, ...) to build with, a few cool items (and a crapton of gems, wich are all ore dictionary compatible if youy want to use them for gergtech use or whatever) give a lots of reasons to explore your world, add awesome looking biomes (and in the nether too, natura compatible there too) wich, unlike EBXL (or highlands (or whatever)) ones, use the sky, fog and water color to give the exact atmosphere they need to have (wich is what makes them really different and better than other mods), making them really pretty (i mean look at the screenshots on the topic), while EBXL ones are just plain good.
Now as i said, it uses a new world type. Adding it won't change anything on old worlds, and allow players to choose to use it or not on new ones. So there is no reason to not add it.
(And if you want to know what i think about highlands, i'll say that it haves the best looking alps biome ever, but i hate the use of vanilla tree logs and leaves to make the new trees (they could have added new blocks and saplings), and the need to craft their saplings with vanilla ones and some stuff. This really bugs me.)
BETTER STORAGE
And then, evryone will say :
-But we already have iron chests. Why add that?
or :
-We should replace iron chests with that.
No. You should understand that those 2 mods don't focus on adding the same kind of storage, even if it looks similar. Iron Chests add storage with large capacities (and a awesome looking glass chest (i don't care how expensive it is, all my chests are glass chests) wich is a good reason to keep it), while Better Storage add decorative storages, safe storages (using an awesome lock and key system with lots of enchants possible) wich make it really useful on servers as an alternative to the IC2 safe, multiblock storage (crates), backpacks that you can carry like armor and place in the world (and they are dyeable), an armor stand (we don't really care about that, bibliocraft haves a nice one), and have a planned features and ideas list wich is full of cool stuff. And used along bibliocraft, it would be a great addon for decorating builds.
TRAINCRAFT
This one had been removed of the modlist of ultimate at the last minute because it was buggy as hell. But the recent versions (1.5.something) include lots of bugfixes (read the changelogs), and i did some testing with them, it works fine. Also, all it's stuff is now forge oredictionary compatible, and the oil distillation thing for oil sands and "stone" now produce liquid fuel that you can use in your combustion engines or boilers, and produces as a byproduct some MFR compatible plastic.
I also did some testing about the supposed superOP steel recipe. All recipes have been added in recent versions, and the steel one have changed. you now need a special furnace, wich costs a crapton of iron, and some nether brick, so like the railcraft blast furnace, you need a nether acess. Then the recipe is really coal-inneficient. A Railcraft blast furnace uses 1 iron ingot and 1 coal coke (so 1 coal), or a few charcoal, wich are really cheap, to make 1 steel ingot. The Traincraft recipe uses for each steel ingot 4 coal and 0.5 clay, and goes as fast as the RC blast furnace (damn slow). And greg's way use 2 coal and some (solar-free-you-cheater) energy. So it's just for eventually having steel before you find slimeballs for your RC blast furnace (it's the hardest part to get), but you'll want to upgrade to another way as soon as you can.
All reasons wich made that Traincraft can't be in FTB (incompatibility, bugs and OP steel) are gone, so why not?
DARTCRAFT
This one is in the No Gregtech version of the 1.5 test packs, and surprises me a lot. It look like one of those weird and stupid mods made by children at the first look (those kind of mods with unrealistic, cheaty and weird/bad looking textures (dartcraft is full of yellow
)), but it's in fact very complete, with lots of cool features, balanced, and very compatible with other mods. It looks weird, but would make a good addition to FTB (but i suppose its' planned as it's in one of the 1.5 test packs).
IMMBIS MICROBLOCKS
Even if Redpower is updated (wich isn't supposed to happen), we should still add it, as, even if it's not as good as Redpower's, it works with mod blocks (supposing the config is done correctly. Adding all the IDs will be a pain), and we need microblocks out of mod blocks. It is also the reason of why lots of modders don't add stairs and slabs versions of their blocks (it's what Powercrystals told me when i asked about stairs and slabs for his bricks). So we need it if we want to be able to build cool stuf out of mod blocks.
THE AETHER (2)
The return of one of the biggest and best mods of minecraft (played a lot with it in Beta 1.7.3). Ok, it's buggy for now, as they're remaking it, but we can just wait until it's fine.
And to anyone wich will say :
-Meh. it don't interact much with other mods.
So does the Twilight Forest. They're the same kind of mod : it's a new dimention to explore, find ressources and build in. They don't add much new ressources wich needs to be compatible with other mods, as they add mostly mobs, building blocks, and some other cool items (food, tools and weapons, ...), and are here to add to the adventure side of minecraft, not the ressource production and use. And i suppose it's stuff is forge ore dictionary compatible (mostly logs, planks and stone, i suppose). I will need to do some testing there.
EDIT 3 (part 2) : I've seen on the TConstruct topic that aether support is planned to be added
GALACTICRAFT
This one is a pretty cool mod, evryone will tell you this, and i heard it has Gregtech recipes if you don't have UE (correct me if i'm wrong). And even if i don't care about the moon, i like to fly rockets in the overworld, until i crash on a mountain. This is fun.
On the other side, it's buggy. Very buggy. So i'm for waiting that it's less buggy and then we add it.
ICBM
Heard it has Gregtech recipes too (correct me if i'm wrong again). This mod is simple. Not much to say about it. It's : Explode all the things, and from far away if you want. And if a serv admin is afraid of seeing his home loudly disapearing some day, he can just disable it.
EDIT 4 :
DIMENTIONAL DOORS
I forgot this one. I'm a bit tired of writing after that giant post, and i suppose you know about it, it's a popular mod. Cool mod, allow interesting building possibilities, and have cool dungeons... Or not. That eye creeped me so much during the testing that i immediately used my overworld emergency backlink (i was in creative, but that's not a reason to stay).
May be slightly buggy, but again, we can wait for it to be more stable.