For use with a computer (at least for dynamically generated content, like 2D desktop work or 3D games), a fixed-pixel display with a digital input and good response time is what you are looking for. Most high-end LCD/DLP/Plasma HDTVs would work well, assuming you can get them to play nice with your video card (avsforum.com has forums with lots and lots of info on this topic). Most of the newer ones have enough pixels to display 720p HD content natively, but not enough for 1080i/p. There are some 1080p LCD HDTVs coming out (or maybe they are out at this point?), but they are not cheap.
For the best video performance, it's hard to beat a high-end CRT like a Sony XBR direct-view CRT HDTV. You could run 720p or 1080i from a computer into one of these as well, but it wouldn't be quite as sharp for desktop work. Computer games would probably look great, though.
The Dell 2405FPW is also a very good 1080p LCD computer monitor that can be used for video display as well. The only problem is that it doesn't have HDCP support, so you can't watch HD content that requires HDCP. It's also only 24", as compared to 30-40" or more for an HDTV.