I don't know about where you are, but here in Austin TX the resolutions are fixed by channel. For example, ABC, NBC, PBS, and WB all broadcast at either 480i or 1080i. The FOX affiliate broadcasts at 480i or 720p. These are OTA only. On the local cable company, everything except FOX and ESPN are upconverted to 1080i - why I don't know. I believe the reason is 1080 is a bigger number than 720 and thus must be better. Finally, everything HD on DirecTV is 720p. Bitrates vary (IMHO PBS usually having the best starting in the evening when they turn off the three other feeds they provide OTA) all the time. The best resource I've found has been the
AV Science Forum which has a rather large listing of HDTV information for various cities.
Finally, to add some fuel to the 720p vs 1080i debate - IMHO: it's all about your output device. If your output device is any type of projection (including rear projection TVs) then p is always better than i simply because that's how your device draws the screen anyway. I could be wrong, but at least it seems that way to me.