The Vanilla mob farm designs still work. The water can be replaced with other methods when playing modded which can greatly increase your pearl output. Mob_grinding_utils adds many helpful bits, including fans to move mobs and a mob masher which can be upgraded to Looting X. Actually Additions has ways to move mobs as well, similar to conveyor belts. XU has various Spikes to kill the mobs, each tier with it's own perks (gold offers XP, while diamond offers player only drops).
I've always been fond of the Etho style Vanilla trap, as it prevents spiders from gumming up the works. It does so by using 3x3 spawning platforms with a slab in the center (spiders need a 2x2 space to spawn). His system, being Vanilla, uses water channels to move mobs, which makes it inefficient for Endermen, however we have more ways to move mobs about than that.
Given the mods at your disposal, a flat dark room with fans pushing the mobs to a single kill box should be doable very early at a relatively low cost. If you keep the floor dirt, you can use XU Drop of Evil to convert it to Cursed Earth, which will spawn mobs even if a player is not present (they will despawn after a short time if not killed), allowing mob farming to continue even if you're not nearby (assuming chunkloading).
