The following is a non-exhaustive list of good websites to download models, textures and other modelling-related files.
- Turbosquid - free and paid models
- 3DRT.com - some free, but mostly paid models.
(A general note for downloading models - make sure the polycount isn't too high, as you will no doubt experience problems using them in your game. High poly counts can slow everything down, and I've seen some old forum posts where clients have actually crashed when the client attempts to load them. Reducing the polycount can be a lengthy task, and you may be better off just modeling it from scratch. Also, make sure you check the licensing conditions on each model's page, as some won't allow them to be used for commercial purposes. Thanks to delurin for that tip!)
- MakeHuman is an open source human model creator, which allows you to take a base male or female model, then tweak settings such as facial features, expressions, ageing, body type, and things like that. At the moment, it's in its early stages, but it is still an incredibly useful tool for churning out a few character models.
- CGTextures - my personal favourite. A huge selection of free textures, all excellent quality. You can sign up for a free account that gives you a download limit of 15MB per day, but for some reason the limit never seems to work, so pretty much unlimited downloads!
Got any more you'd like to suggest? Just reply with the name, link and a description, and I'll add it in.