Just make sure the HDTV you pick has a good scaler/upconverter built into it otherwise you will be unhappy, not just with the Wii but with basic t.v. channels as well.
When you go to buy one make them put standard definition, enhanced definintion, and high definition on it so you can see how well all the current formats look on it. This is a transition period between the formats, so for the next 5-10 years your gonna need a t.v. that can handle all of them.