Do you have to have a groom's cake and a bride's cake at your wedding?
No, you don't have to. The bride's cake is the one we generally refer to as the wedding cake -- the one you cut and feed each other. While this cake is traditionally lighter (yellow or white cake) with light-colored frosting (although it can be made of anything you want these days!), the groom's cake is traditionally a darker, heavier cake. Many couples who do have a groom's cake make it a special "theme" cake for the groom, maybe shaped like something that reflects his job or a hobby.
As an aside, the tradition behind groom's cakes custom is this: Slices are sent home with guests in little slice boxes (they can even be your favor), and single women are supposed to sleep with the slice under their pillow that night (ick -- nice hair in the morning, huh?). Legend has it that they will dream of their future husband.