Depends on the size you want, and the resolution you want.

If you want to go the whole hog and get a 1080p HDTV, then it'll be over the 40" mark, and cost around $2500, I guess.

You can get 720p HDTV's, though, for a damn sight cheaper. I reckon you can get a good 32" one for about $1000. Most of this is just guesswork, though. I'm going off UK prices and just doubling them to get dollars, but we pay a lot of tax on technology, so I'm probably way out.

In fact, here are a few Samsung's from Amazon. I thought you might want white to go with the 360.

Samsung 19"

Samsung 23"

Samsung 26"

The third one is part of the range I got mine from, I think. Very good TV's. All three have HDMI ports, btw, and they might have serial ports, so they can be used as monitors.