Breeders Beware Contains a wide range of content for Creatures 3 and Docking Station, including downloadable environments, breeds, objects, along with tutorials and other resources for people who would like to develop their own mods.
Sims2Pop A collection of modded objects and Body Shop content for The Sims 2. The majority of downloads are Star Wars themed, with a particular focus on the era depicted in Star Wars: The Old Republic. Other downloads focus on bringing new playable species to the game. This site does not include the few downloads that I have uploaded to Mod The Sims.
Weatherfac/Pyro's Sims 1 Repository Hosts a handful of downloads for the original The Sims game.