Depends on what you want to spend. I have a JD LX255 that I've been very happy with, about $2500 - $3000 (I think). The Kubota mowers were really nice but quite a bit more money. My neighbor has a Sears lawn tractor that he beats up pretty good - it is showing wear and tear, but still works and he paid less than $1500 (don't think they make bigger than a 48" deck - might go to 54", I'm sure they don't have a 72") model. Another neighbor went the ZTR route - bigger lawn - and paid something like $6000 for a used model.
All the other suggestions are good ones, too. How can getting another tractor be a bad thing /forums/images/graemlins/smile.gif?