Excellent! I might have to get an iPhone after all... ;-)
If you already own a GPS unit for your car, there are online sources for the speedtrap/redlight camera locations that work with most units. One I've used is at trapster.com; it allows you to select the areas you travel in. As people upload new info, you get update alert e-mails.
Works like a charm - and the data stays fairly current. You get a little chime noise when approaching a reported site, along with a small text box describing the possible threat. I just leave the GPS on in "map" mode. The first week I used it, I heard the chime and sure enough, there was a motorcycle cop hiding right where it indicated.
As the law enforcement agencies realize they're being out-teched, they'll resort to moving their ambush locations more often.