Flax & Wheat: Redpower. Two deployers at the bottom, with 0,2 second delay between them, one with seeds, the other with bonemeal. Blockbreaker also at the bottom, set to 0,2 delay more than the two other deployers (so 0,6 seconds), hooked up to 2 filters, one feeding seeds directly into one of the deployer with a restriction tube for storage, and the other delivering the wheat/flax to your sorting system. Bonemeal can be achieved by T3/4/5 Skeleton Spawner or Sulfur Goo farm.
Sugarcane/Cacti: Either golems + Xycraft Soil, or stack a LOT of xycraft soil - like 30 or more - and use a timed block breaker to harvest the sugarcane at the second block, feeding into your sorting system.
Melon/Pumpkin: Make the block to only be able to be grown at a single spot. Redstone cabling up to the spot where the melon will grow, with a redstone signal, and more redstone on the other side, leading to the block breaker. When the melon grows, redstone signal gets transferred to the block breaker, and it harvests the melon/pumpkin. Easily automated, no need for golems, flux, or anything else... apply Xycraft soil beneath the stem for better results.
Cocoa: AFAIK Multifarms do this better than anything else.
Mushrooms: Mycelium + Multifarms gives you the best yield, i kid you not.
Netherwart/Potato/Carrots: Golems or Multifarm.
Wood: Steve's Cart if you want apples & oak wood, or if you want a different kind of wood, if you're satisfied with Fir Wood, i'd give priority to Turtles + Ultimate Wood Chopper program (CC forums). As a bonus, the CC program is also set up to give you a whole shitton of Charcoal, and you can easily expand the system.
My opinions:
Flax & Wheat i'd do with Redpower. Simpler, easier, less expensive, requires no power.
Sugarcane/Cacti i'd do with Xycraft soil + redpower. Simpler, easier, less expensive, requires no power.
Melon/Pumpkin i'd do with Redpower: Simpler, easier, less expensive, requires no power.
Cocoa/Mushrooms/Netherwart/Potato/Carrots: I'd go with Forestry's Multifarms. Best yield, set & forget.
Wood: If i wanted apples, or wood as building mats, Steve's Carts. If i just wanted wood for the mats for recipes, i'd go with CC, because Charcoal is also a boon.
Other products;
Walnuts/Chestnuts: You have to go Forestry. There's no other way.
Apples: Steve's Cart or Orchard from Forestry. Steve's Carts is more efficient, because it also gives you wood, as already noted.
Cherries: Forestry, same reasons as walnuts/chestnuts.