I was in the market for a used mower about 4 years ago. I wanted a zero-turn mower, but found that I could get more bang for the buck by settling for a standard format Kubota riding mower. It has a 60" deck, a 19 HP diesel engine, and a hydrostatic transmission. The drivetrain is totally sweet - a real pleasure to operate. It is not as fast as the zero-turns I've seen but I can cover some ground with it plenty quick. Probably more comfortable than a zero turn.

As for zero-turns, I think there is a big difference between the Home Depot versions and the true commercial mowers. I helped my neighbor with his Home Depot zero turn (the white and yellow type - Cub Cadet?) and found the skid steer to be more difficult and less intuitive than the commercial grade Ransons I used a few years ago.

Whatever you get, make sure it has plenty of power and a good, high-speed mower deck. Those are the keys, IMHO.