ChessVideos TV-You can practice chess endgames against the Crafty engine against a large variety of puzzles in all difficulties.
Chess Endgames-Thousands of interactive endgames, 32-round endgame challenge, mate in 2, 3 and 4 and problems. Sign Up required. It's Free!
ChessTempo-Tactics training site including endgame training.
Chess Kit-basic endings, Pawn endings, Rook and Pawn, Four pawn endings, and more.
Shredder Endgame Database-allows you to setup any position with 6 men or less to get the true results of the position.