Hotspotr is now available as an interactive map on your cell phone. You can browse for WiFi hotspots on the go -- which is exactly when you need to find hotspots right? See the link on the home page, or jump right to the mobile download.
The mobile goodness is provided through a partnership with LightPole. I tried several similar mobile services, and LightPole is doing a fantastic job. I've been using the application for some time myself during development.
Note that you have to be on Sprint, AT&T, or T-Mobile, and that the app is free. give it a try.