Get as big as your budget allows.
Best bet is stay with brand names - Samsung, Sharp, Toshiba, Sony are all good bets. I'm not so crazy about Vizeo or Olivia.
I'd agree with all of that.
Go in the store and look at the sets and see what looks good to *you*. Make sure they are hooked up to good sources and don't be afraid to ask for the remote and make adjustments in the store. They may look at you like you're crazy but you won't end up at home with a $2000 TV set that you're less than happy with. You might want to bring in a DVD or two of the type of material you will normally be watching. Do remember that how a TV looks in the store isn't always how it will look at home so be mindful of that when looking at a set 15 feet up in the air among 20 others.
If you go with a chain like Best Buy or whatever you do have the option to get a different set within 30 days if you aren't happy. That can be great peace of mind on a first HD purchase worth whatever savings you might be able to get from online or warehouse retailers.