An awesome in-depth article covering modifications spanning many games have just been posted @ Gamespot. This article entitled, 'Its a mod, mod world' spans 7 pages and discusses some of the more prominent popular mods from all the great games currently supporting the mod community. To give you a taste of what to expect, here is a chunk from the intro
Marc wrote: Why just play games when you can make them? That's the idea behind creating game modifications (or "mods," for short), an increasingly popular activity among savvy computer gamers looking to build an all-new experience using their favorite games. And we're not just talking about new maps or skins here, either. Mods often go above and beyond new levels or graphics by changing the gameplay itself (referred to as "total conversions"), and they can also add new characters, weapons, and storylines into the mix. You always need the original game to create (and, of course, play) a mod, and afterwards, the finished product is frequently distributed using the Internet.
This really is a fantastic article, and must be read. The best part however, is at the end when he writes 'The following Web sites (not listed in any particular order), cater to the passionate mod community.'
Somehow, modDB managed to get a mention here, so the word really is spreading and sure he may have gotten the link semi-wrong, but any promotion is good promotion, so rock on i say! :P