Free PC Games
acid-play.com 
Freeware games site.
Top Ten free games Hall of Fame
Software4free presents the ten best free downloadable games available - stable, up-to-date, well supported, user-friendly and well documented.
The Battle for Wesnoth
The Battle for Wesnoth is a free, turn-based strategy game with a fantasy theme.
remaininplay.com
Tries to catalog all commercial games that have been turned into freeware games by their copyright owners.(sometimes source only)
www.free-games-net.com
Click the games link on the horizontal menu for a full list of the free games available.
www.freewaregames.net
Freeware games with direct downloads, reviews, and top picks.
GameHippo.com
PC freeware games to download (no shareware or demo games)
Free Computer Games A-Z
A lot of these are demos or shareware, but there are some free ones too.
Free-Games.as
Archive of freeware pc games, sorted into 12 categories.
megagames.com
An index of games including freeware, demos, cheats, trailers, etc.