Lately I've been playing a lot of Tekkit. For those who don't know what Tekkit is, it is a set of Minecraft mods that add things like quarry's, solar power, copper wires, oil, etc. Heres a link to the thread: http://www.technicpack.net/tekkit/
It is VERY easy to use, all you do is simply download it to your desktop or wherever you want to access it and run the launcher. In addition to Tekkit you get other mod boxes like Yogbox and Hack/Mine.
Reason I bring this up, I was wondering if anyone else uses this and would like to play multi-player. If you run a server Feel free to post it in here. I tried to run one, but I lag too much.