Just a fast mention to this discussion group (I’ve already suggested them to Fencer) of my three favorite chess variants--ones that I would like to see here, someday...

Alekhine Chess
Played on a 14x8 board, this variant includes three non-standard piece types: the Cardinal (Knight + Bishop), the Marshall (Knight + Rook), and the General (Knight + Bishop + Rook).

Inheritance Chess
In this variant, the white rook pawns begin on the third rank and the black rook pawns begin on the sixth rank, castling is not permitted, en passant captures are not permitted, and, most importantly, pieces have inheritance powers.  Pieces of a given color on the same file inherit the movement powers of one another.  These powers do not stay with each piece for the entire game; the inherited powers are only inherited while the pieces are on the same file as one another.

The Lost Pawns
In this variant, white's pieces actually start on the 7th and 8th ranks, and black’s pieces start on the 1st and 2nd ranks, with the direction of the pieces remaining the same as with a standard chess game.  In other words, all pawns are just one square away from promotion.  Two-square pawn advances and en-passant captures are obviously not possible since all pawns start on their 7th ranks.