From the Creators of Shockwave and Flash. Has many arcade classics like Rampage and Spy Hunter
Shockwave

Free Stuff Center. These guys only have four games but they are high quality ones
Free Stuff Center

Has many games, check it out.
http://games.2nd.net

Flash Arcade contains many high quality games and various other flash progrems
Flash Arcade

Has some good quality games. The links are on the right side of the page.
http://www.real.com/

Really neat site run by Life Savers.
http://www.candystand.com

Another Shockwave/Flash game site.
http://www.nabiscoworld.com/