Google's My Location technology is cool. When I'm using my iPhone, I just hit a button and it gets a pretty close assessment of where I am, using cell triangulation (yes, I still have a first gen iPhone).
Now, Google is outfitting My Location with the ability to use WiFi access points in determining location. The feature is also included on the Gears Geolocation API.
Blackberry users can download the newest version of Maps for Mobile to access this feature. Other mobile devices will get the feature soon.