Berries -- Web-based game in which the object is to knock out the other (computer) player by converting their berries to your berries.  This is done by putting a berry next to their berries.  Kinda fun!
The Bingo Zone -- Registration is free, all the games are free, but you play to win cash prizes.
Cyber Arcade -- You can play for free and win tokens, which are redeemable for prizes.
duJour.com -- Loads of exciting free games with chances to win prizes.  The games are changed every 24 hours, so you never get bored!
FOP Online '97 -- Pick the most winners of NFL games of the week and win $100.  Large cash grand prizes for the players who pick the best winning percentage over the course of the season.
Flipper -- Web-based game in which the idea is deceptively simple, yet belies its complexity.
The Gamemaster -- Just register, and play  lots of free games to win prizes.
The Logic Board -- Web-based game in which you try to guess a sequence of four colored pegs in the correct order in ten or less guesses. For each guess, black and white pegs will be awarded: one black peg for each color you have guessed correctly in the correct position, and one white for each color you have guessed correctly, but in the wrong position.  A lot like the board game Mastermind.
Riddler's Games -- Yes, it's FREE!  All you have to do is register to play!  Word games, card games, trivia, sports trivia, riddles, multiplayer games, and much more.
Trivia Blitz -- If you have a Java-enabled broswer you can play this free trivia game.  You must answer quickly and if you score 1500 or more points you qualify for a weekly drawing awarding $25.  You must have a valid Oasis Games name and password to qualify for the drawing.
Trivia Hound -- Answer the daily trivia questions for an opportunity to win prizes.
Yoyodyne -- Loads of games you can play for free to win prizes.