Well, I have a JD LX255, which has all the features you're looking for (HST, 42" deck, etc.), although I think my motor is rated by JD at 16HP. HOW-ever...my neighbor has a Sears tractor that is rated at 20HP, and I've spent a fair amount of time on that seat. My JD will out power his Sears any day (and he agrees with me).
I'm on 10 acres and I use a Kubota tractor with a brush hog for most of the grass. Near the house I use the JD, and it does a really nice job doing finish mowing. Every now and then I decide to mow some more stuff when I'm done with the yard and I take it out into the areas that I usually use the bigger tractor for. This usually means that I will be sharpening the blades soon... /forums/images/graemlins/crazy.gif
The JD performs like a champ. It isn't 4WD, and has turf tires so there are times that I lose traction, but I never run out of power, even when plowing through deep grass (a foot or more). The mower will sometimes bog down on me (it is a 42" deck), but has never stalled the motor.
We use that thing all the time - at least as much, if not more than the Kubota. When we aren't mowing (and we have about 1/2 acre of "finish mowing" that has to be done at least once a week), we use it to haul a wagon for firewood, mulch, gardening, kids... even use it to go visit the neighbors (long walk, up hill /forums/images/graemlins/smile.gif).
Can I say anything more nice about my JD lawn tractor? /forums/images/graemlins/grin.gif
Oh, I don't remember the exact price - it was a lot more than a Sears machine, but has some features that the other one doesn't, like a solid front axle, and stuff like that. But I think it falls within your price range, and there are other JDs that are less expensive (but may not meet your other requirements).