With that price range, you may be best off getting one of the better 22" TNs for around $300. I would suggest the LG L227WTG-PF, which is available at Best Buy. It has a glossy coating and minimal motion blur and input lag for an LCD. I think the pros of the coating far outweigh the cons, but you should take your room's lighting setup into account before buying it.
The 24" 8-bit xVAs (or the excellent 26" DoubleSight IPS) are more around $700. I only know of one 8-bit 20" model that you can still buy, the HP LP2065, and there is a panel lottery going on with it. There are also several 24" TNs for $400-500, but the low viewing angle is an issue there and you'll get subtle color shifting at one edge wherever you look at them from. Note that the 24" models have a higher resolution, which looks better but also means that you have to upgrade your video card more often to keep up with it.
As far as the panels go, there are different advantages to all three types. TNs have low viewing angles and can't display the full 8-bit color space, instead using dithering and flickering methods to simulate it. This works well on still images but less so on moving ones. I can see the dithering prominently on Lightspeed's nebulas in FS2, for example. However, they also have lower motion blur and input lag in games than xVAs, to a greater degree than the response time numbers would suggest. IPS panels are 8-bit, have perfect viewing angles and are still almost as fast as TNs, but they're rare on consumer market LCDs these days and have somewhat worse black levels.
