If your seating distance checks out, get the 50PX80u. 1366x768 pixels is more than enough at any distance beyond 6-7 feet of so, and the panel itself is fantastic value. It easily outclasses everything else in its price range, and blacks better than nearly every other set push its PQ above countless other more expensive 1080p sets from lower tier manufactuers. If your only spending $1000 bucks, getting good black level should be your primary concern, not step-up resolutions that do little for the picture. There are other real PQ enhancements packaged in to the higher-priced 1080p plasmas, but they generally have nothing to do with resolution.
Another set you could look at is the pn50a450. I view this set nearly every weekend at my friends place, and while I find it pretty good, its blacks just aren't quite at the same level as the panny. My friend loves the thing though, and now despises his old lcd, which was a $4000 sony xbr2 with some pretty poor blacks and a whole lot of clouding. He sure doesn't miss 1080p.
Also, don't get a 42 incher. Thats not a very good HT size, and your room can easily handle bigger. I agree with everyone here and would say go for 50 inches.