This is just my opinion, so take it as an opinion only, not fact.
If I had a $4000 budget to work with, I would be getting a DLP HDTV set. I like DLP because most of the rainbow and other issues that the first generation had have been worked out. They are still not perfect, but definitely good enough for me. They are very bright, very crisp pictures, and they have NO SCREEN BURN IN. That would be very important to me especially if you planned on using the TV for a lot of gaming. LCD TV's have size limitations at this point and are very very expensive. Plasma has gotten a lot better all around, Picture Quality, Black Levels, and even screen burn-in. Still, Plasma HD sets are more expensive than DLP sets are and still have sreen burn-in capability. I would rather go with DLP and get a much larger TV.
I think you meant to say 1080p. I myself would not wait for 1080p as programming for 1080p may never come, and if it does, it certainly will not be for awhile. If you did get a 1080p set, you would be paying a large premium to have all 1080i material upconverted to 1080p, not much of a noticeable difference in my opinion and certainly not worth paying a large premium for.
A DLP set will be 720p which will be great for gaming and is great for High Definition television programs as well. I myself have a 1080i set, but would prefer the stability of a progressive scan field as opposed to an interlaced one. This will help with fast moving video games and fast moving object/programs on TV such as sporting events.
To sum it up, I think the best bang for your buck would be to go with a DLP based HDTV. I'll let you figure out what brand to buy and what size to go with.
Good luck!