Here's a list of available radios
http://forum.ppcgeeks.com/showthread.php?t=46616
Most popular seem to be the Telus 1.04 and the Sprint 1.11f, the US Cellular is the newest that I'm aware of. Since it seems you've already unlocked and flashed a rom, flashing a radio is a walk in the park
Keep in mind that unlike a rom, a radio flash is non destructive. You should back up your data just in case, but flashing shouldn't causes any loss of data. Since location seems to affect which radio works best, you may want to try out 2 or 3 of the most popular to see which works best for you. Have fun!