Most games don't manage 1080p anyways, so if you don't have the money 720p should suffice.
If you want to "future proof" your tv, then go with a 1080p tv, as I'm sure next generation most games should manage 1080p.
edit: oh, and unless you are sitting awefully close to your tv (8ft maybe) you will barely be able to notice 1080p anyways.