Transcendent chess is a strong variant to add to the chess arsenal. A precursor to FischerRandom chess, both backfiles are shuffled, and are separate from one another. It may require some tweaking, as it has an option to transpose 2 pieces as the first move, instead of castling. There is no castling in TC. Also they are played in pairs, with the same position, and players take opposite colors.

There is an Auction TC where you can bid to see who goes first, and you can offer up a certain number of moves if you are feeling certain you can win with a particular position.

I see the list of games above, but I wanted to throw that one in.

Also, I would like to see Alice Chess (posted at Chess Variants: Alice Chess) and consists of 2 boards side by side. Pieces powers are as in "normal" chess, except that when they move, they disappear from one board and appear in the same square on the adjacent board. Moves must be legal on the "exit" board, and then the piece moves to the "enter" board, back and forth on each turn. Mate becomes harder to see, and plans take an odd turn. Interesting to see a CC version of this; I am not sure how much of a challenge programming would be.

I thought I would ask.