Here are some freeware titles for the PC, consisting of both games that have always been free and ones that were originally for sale but have since been made freeware. Most of them are downloads but there's a few browser games in there. This list does not contain any free to play games. (Sorry TF2.) Currently working on adding download links.
Some links that may be of interest:
- Free Gamer (Freeware news. Includes a giant list of free games.)
- Liberated Games (Lists former commercial games that are now free.)
- TV Tropes page on Freeware (Groups games by platform and genre.)
- /v/'s recommended freeware games (Huge list with descriptions and download links.)
- List of freeware games on Wikipedia (Self-explanatory. There's also a freeware category.)