I read a few good posts over at the High Definition Blog regarding signal & screen resolutions as well as the "progressive vs. interlaced" debate. These are excellent articles and well worth a read instead of standing in shopping lines today!
Give 'em a view and then let us know what your preference is for high-def display resolutions. It can certainly depend on the type of content you have; but if you have a deep love for one over the other, let us know. I can definitely tell a difference between my 720p feeds from Fox and ABC as compared to my 1080i feeds from CBS and NBC. I prefer 1080i as it appears noticeably sharper. How about you?