Tile chess maybe? a box n (Usually <5) boards high stack on top of each other. You can make one move on a board, or you can "tunnel" a piece to a board immediately above or below it on the same square. Pieces can be captured this way, and can give check. Kings are normal pieces until you only have one left, and the laws of chess apply. I personally like the 3 board version of this one ;)
More chess variants (also avaible at Live chess?)

Switch chess : You start normal, and pieces move normally, and the idea is to checkmate, but a move is also legal if 2 pieces switch with another. You can only switch captured pieces with a non-captured one ;)

Atomic is nice. In atomic, a capture also removes the capturing piece and the pieces on all 8 surrounding squares (like an exploding atomic bomb).
This leads to nice variations such as 1.Nf3 Nf6 2.Ne5# mate; black can't defend against both Nxd7 and Nxf7, both of which would remove the king on e8. Therefore (I think) 1.Nf3 e5 is forced, and now if white were to play 2.Nxe5, his knight is gone so there is no mate.
Often the center is quickly filled with pawns (like 1.d4 d5 2.e4 e5) that stay for a while, since a capture would place themselves in check (3.exd5 isn't possible because 3...Qxd1 captures the king).
Hmm. I just checked Wikipedia, and it says that pawns aren't removed. Well, then I used to play a different version :-)

The black and white pawns are switched so that all the pawns are one step away from capturing an opponent piece and getting promoted. The game can start, for example: 1. Nc6 Nf3 2. b8Q g1Q etc.
1. dxe8 and the game's over

The black and white pawns are switched so that all the pawns are one step away from capturing an opponent piece and getting promoted. The game can start, for example: 1. Nc6 Nf3 2. b8Q g1Q etc.
1. dxe8 and the game's over
His first sentence is wrong. The set up is the same as for normal chess, however, the direction of the pawns is reversed. That is, your pawns are coming towards you instead of going towards your opponent. So you can't move any of your pawns to start. You have to move a knight, and then you can move a pawn into the space where the knight was and promote it to a queen.

The black and white pawns are switched so that all the pawns are one step away from capturing an opponent piece and getting promoted. The game can start, for example: 1. Nc6 Nf3 2. b8Q g1Q etc.
1. dxe8 and the game's over
His first sentence is wrong. The set up is the same as for normal chess, however, the direction of the pawns is reversed. That is, your pawns are coming towards you instead of going towards your opponent. So you can't move any of your pawns to start. You have to move a knight, and then you can move a pawn into the space where the knight was and promote it to a queen.
Ok, I was quite confused there for a moment.

Omega chess, I have been playing it on an e-mail games server for a while now. It's almost like an expansion of a regular board and setup.

Hmm... I wonder if there is some kind of variant, where you play 2vs2-team match, both are same colored, but it will be played on 2 boards AND set-up is symmetrical? (like this:
) (think those boards are aligned each other horizontally...)
The black and white pawns are switched so that all the pawns are one step away from capturing an opponent piece and getting promoted. The game can start, for example: 1. Nc6 Nf3 2. b8Q g1Q etc.
1. dxe8 and the game's over
His first sentence is wrong. The set up is the same as for normal chess, however, the direction of the pawns is reversed. That is, your pawns are coming towards you instead of going towards your opponent. So you can't move any of your pawns to start. You have to move a knight, and then you can move a pawn into the space where the knight was and promote it to a queen.
That sentence was copied straightly from Wikipedia...

The traditional "extinction chess" variant that I know has a different winning condition: capture of all pieces of the same type (ie. both B's, both N's, both R's, the K, the Q, or all 8 pawns) wins. It's quite playable, avoids book, and demands at least as much skill as regular chess ... perhaps more skill tactically.

I just recently published a short fantasy story on the Amazon Kindle featuring a number of new chess variants that I developed:
"The Amnesiac's Quest" (available on the Amazon Kindle for 99 cents)
Here are some of the variants portrayed in the story:
Promotion Chess
Attrition Chess
Melee Chess ("Chesskers")
Diamond Chess
Parasite Chess
Most of these variants would be challenging to play unless one had multiple identical chess sets, since they use more than the standard number of each type of piece. This is because in many of these variants, each piece has the ability to change its rank to become another type of piece based on what it does in the game.
While trying to play these variants, I realized that I had to make my own chess set that would allow me to quickly transform one piece into another. The result?
Chess Cubes! (available on Etsy.com)
I've made a few sets of Chess Cubes, and they're available for sale on Etsy in two varieties: "Psychedelic", and "Coal and Marshmallows".
If you are interested in trying out the variants from the story, then my hand-crafted custom-made chess set is the perfect way to do it.
Transcendental chess:
Similar to chess960, but the opening white and black positions do not mirror each other.
Upside-down chess:
The black and white pawns are switched so that all the pawns are one step away from capturing an opponent piece and getting promoted. The game can start, for example: 1. Nc6 Nf3 2. b8Q g1Q etc.
Cylinder chess:
Played with A and H files "connected". Thus a player can use them as if the A file were next to the H file (and vice versa).
Three checks chess:
You win also if you check your opponent three times.
Suicide chess:
Capturing moves are mandatory and the object is to lose all pieces. There is no check - the king is captured like an ordinary piece.
Handicap chess (or chess with odds):
variations to equal chances of players with different strength.
Weak!:
White has usual pieces, black has king, seven knights and sixteen pawns. This game was played at Columbia University chess club in the 1960s.
Checkless chess:
Players are forbidden from giving check except to checkmate.
Crazyhouse:
Captured pieces change the colour and can be dropped on any unoccupied location.
Andernach chess:
A piece making a capture changes colour.
Extinction chess: A Player must capture all of his/her opponent's pieces to win.
Knightmate (also called Mate The Knight)
A game invented by Bruce Zimov in 1972. The goal of the game is to checkmate the opponents's knight (which is placed on e-file). The kings on b- and g- files can be captured as other pieces. Pawns can additionally promote to kings but not to knights.