I rather like the major tech mods out there like Buildcraft, Industrialcraft, Redpower, Forestry, Thermal Expansion, Factorization.
Computercraft, Portalgun, a bunch of IC addons and Railcraft, Mystcraft, ExtraBiomes XL are some other ones I like to play with too.
http://feed-the-beast.com/
Is a recent modpack that came out for 1.4.2 you can try, if some of those mods I listed interest you but you don't want to set them up yourself. It includes a bit others too, you can mess around with. I don't play it myself though, I have my own blend of about ~40 or so mods.