I found a neat site:

http://evdomaps.com/

From the FAQ :

EVDOmaps.com is a free service of the EVDO Experts at 3GStore.com and EVDOinfo.com, the proud host of EVDOforums.com

EVDOMaps.com is NOT meant to be an authoritative "coverage map".
It is a site where members of EVDOforums can post actual speed test results and descriptions of their gear, so that others can see what service was like at that moment in time, from that user's location.

The objectives of this free tool are:

1) See new EVDO Rev A areas before they are officially announced
2) Determine which areas may be "overloaded"
3) See how our antennas and amplifiers may help in specific locations

They also have some good info in their other forums : EVDO Info, EVDO Forums, EVDO Blog

You can get to them via the link above.