AddictingGames.com
Games galore for people with time to spare.

Asteroids
One of the classics.  Don't try and fly around, just turn and fire like crazy.

Best Crosswords
Free new crosswords every day that you can print out or complete onscreen.  You can even get some help if you're stuck.

Classic 80's Arcade Games
Try some of these golden oldies.

Gamehouse Games
Lots of puzzles and games that you can play online for free.  You can also download trial versions of their super games for free.

Games Market
Find games for your PC, Mac, Playstation, XBox or Gamecube.

Play 500 Online
500 is a bit like Bridge for beginners.  You can play it online here, by yourself or against others.

Smiliegames.com
Lots of great games to try including the classics Galaga and Space Invaders.

Sudoku
All things Sudoku.

Yahoo Games
Lots of games that you can play on your own or against other anonymous surfers.  You can generally choose the level, from beginner to expert.  When this link was added there were over 140,000 people playing various Yahoo games online.