Wow, Street-Level Maps from Cingular!
I'm not sure this was designed for the general public, but it got out on Howard Forums that Cingular now has a Coverage Viewer that lets you type in a street address or intersection and gives you a map with the approximate signal strength in the general area. (Edit: Cingular now has made this a legitimate feature on their website.) Coverage provided by roaming partners also shows on the maps, but you do not get a sense of signal strength, only the sense that your phone should work "on-street or in-the-open" at that particular location (i.e. not in a car or building).
There is some debate on how "accurate" these maps are from Cingular. In some cases, they overstate, in others they understate. Similar complaints have been levied at T-Mobile's Street Level Maps, I'm sure. Both carrier's maps seem to do a good job in my neck of the woods, but your experience will vary. Just remember, folks, it's a guideline. A lot of things both inside and outside of the carriers direct control can affect whether or not you can make or receive a call in any particular area.