I don't see any threads like this around here so I thought I'd make one myself. I've racked up a list of mods for several games you might like to try.

This list currently includes the following games:
GTA: San Andreas
Elder Scrools: Morrowind, Oblivion and Skyrim
The Sims 2
Fallout: New Vegas
Neverwinter Nights
Phantasy Star Online

Pastebin:
http://pastebin.com/0kGjJDCe