Just going off of what I've seen and read here and there:
Mitsubishi Diamond series DLP would be worthwhile to look at. From what I've heard and read is that they're reliable, built well, and have a very good picture (neighbor has one). I own a Samsung HLR-5067 and have been very happy with it. I've learned how to tweak a few things and think the picture quality is superb. I've not had any issues with mine nor has my neighbor had any with his. If I did it now, I'd probably look at the Diamond series first and the Samsungs second.
Of course, I would not put a center channel directly on top of it because it isn't built to support one. I don't think this would be a wise decision on your part to do. Another option would be to place it below the TV and angle it upwards. The TVs are probably designed with the assumption that it will go into an entertainment unit with a place for a center. The center channels can be extremely heavy and I think you'd be hard pressed to find many TVs that can continually support the weight of a good-sized center. Just guessing, but I'd go with the thought that any TV currently manufactured is going to suffer some sort of bowing issue across the top (not the picture, but the frame) because of materials used.
Are you dead set on a DLP? There are other options around.
-pat