I know this isn't in the correct suggestion format, but have you thought of some of the industrialcraft addons? Rocket science and modular forcefields are good ones. ChemCraft is also a cool looking mod, dunno the link to that one though. (the updated one anyways) It works with industrialcraft.
I enjoyed it, it actually would be kind of cool if buildcraft/industrialcraft/redpower created pollution and such that could visibly and physically harm the environment.