Someone in our neighborhood has one of these: a JD SST16. It is a zero-turn lawn tractor. Pretty cool! It looks different than other riding mowers (the hood slopes down more). I know Cub Cadet also makes one like this. (Pictures of both attached).
John Deere: (http://www.machinefinder.com/images/machines/03/2084903/3095565_huge.jpg)
Cub Cadet:
#2
lawn mower fanatic
The difference between the Cub and the JD, though, is that the JD has front caster wheels and the Cub has normal ones.