Fallout 2.5
These'll be of little interest to the more ardent Fallout 2 vet, who's doubtless played all of these long ago, and is already preparing to spam-cry 'OLD!' below. If, however, if you're coming to the game fairly fresh or are replaying it for the first time in ages due to excitement about Fallout 3 or because GoG.com's made it so cheaply available, you might find much to delight and enrapture your young mind here.
It's Moddb's round-up of the best Fallout 2 total conversions, from the quest-expanding Restoration project to the tri-part Wasteland Merc series. Oh, for more free time.