Trivia:
General
Entertainment
Movies
Sports

Text Games:
Slimewars - Star Wars parody

Traditional
Blackjack - see who can get the highest number under 21
Checkers
Hangman - current topic is "Presidents of the USA"
Magic 8 Ball - see what it has to say to your questions
Paper Rock Scissors
Peg Solitaire - try to get all but one peg off the board
Tic-Tac-Toe - 4 levels: very easy, easy, average, and hard.
Towers of Hanoi - stack the disks in order from largest to smallest - sounds easy, but it's challenging

Educational:
Typing - see how fast you can type