Thanks in advance!
http://skyrim.nexusmods.com/
I'd suggest downloading the Nexus Mod Manager (see top of page - it says Install NMM).
The nexus site has a LOT of mods to trawl through, but there are several series on Youtube that look at the best. Gophers "Skyrim Mod Sanctuary" is one of these and is always featured on the Nexus homepage! Just scroll down a bit and watch his series (I know watching all of it will take FOREVER, but it's worth it!)
Also, http://www.skyrimgems.com/ and http://testg.wikidot.com/skyrim:skyrim are useful resources.