Shockwave - a cool site with lots of stuff: games, cartoons, etc.

Microsoft Gaming Zone - Tons of multiplayer games, from chess to Quake II.

Riddler - Original games, such as Dragrace, a puzzle game; and Copycat, a Memory-type game.

World Opponent Network - Loads of games, like You Don't Know Jack: The Netshow

Realms of Despair - an excellent, addictive MUD.

Music/Musicals