Well, just yesterday I finally got a real start on progressing to my ultimate Minecraft base (a sky fortress - originality, yay), but today I just had a thought - in what ways (mods, etc.) do you add to minecraft in order to make the experience more enjoyable?
Aside from IC2 (otherwise, I wouldn't be here!), I've used EE2 to get all the materials (hereafter called "mats") I need to start building my base. From Buildcraft, I've used Automatic Crafting Tables and Pumps to speed assembly and fuel geothermal generators, respectively - having logistics and teleport pipes helps even more. Though I have Redpower and Forestry installed, I haven't really used anything from either as of yet (though I've fed all matter of new ores to my relays from EE2 to get up to speed), but I plan to use Forestry's raincatchers for cooling and RP for wiring, in addition to wireless redstone for long-range stuff. Computercraft will also help lock my base down and run the general activities of the fortress when it's all said and done.
As for addons to IC2, I'm currently using CompactSolars for performance reasons, and, once they update (if they haven't already), the Buildcraft/IC2 crossover and Rocket Science mods will be added posthaste for more energy, and to turn my fortress into a flying nuclear silo to rain down destruction upon hapless creepers. >=D
With that said, how about the rest of you guys? What do you use in addition to IC2 to have a great time, be it new content or just aesthetic overhauls?