There are a variety of good mods out there, depending on what you want. The above posts have mentioned many of the excellent UI overhaul mods, and if you want a basic balance mod then VEM/UOP are great. If you want something that adds a bit more content, there are quite a few of those; NiGHTS, Call To Power, and my own mods (see .sig) are pretty large, but there are many others depending on your personal tastes. The key thing, though, is NOT to depend solely on the in-game mod browser. It really has no way to see which mods are being maintained currently, and you won't get much good information about the specifics within each. Some mods (again, like my own) aren't even available through the in-game browser for various reasons. What you should do, instead, is go over into the Creation & Customization forum of this site, go into the various forums (especially Modpacks, Mod Components, and Projects) to see which threads are currently active, and use that to see which mods are being well maintained. That way, when you go to the in-game browser you don't have to just search randomly.