I just found a cool new app called Signal by planetbeing.
Signal is a Cydia Store app I wrote for jailbroken iPhone 4, 3G, and 3GS that shows you interesting data about your cell reception as well as plots a map of your nearby cell towers. Compare coverage between different carriers, test antenna vulnerabilities on your phone, or determine your nearest cell tower. Radio engineers will also find being able to see the downlink and uplink frequencies and scrambling codes of neighboring cells useful for field testing.
You can get it in Cydia for $5 on your jailbroken iPhone.