Greater City: Providence has a post on some recent LED lighting news (good stuff+links in the blog and the comments), including links to a couple of articles on LED streetlights in NYC, Ann Arbor, and others:

Since LEDs use less power than existing halogen, incandescent, or even fluorescent bulbs, it makes sense that this will be the choice in illuminating miles and miles of roadway. Moreover, when cities and states start ordering LED based street-lights, the quantity needed will no doubt force down the cost, eventually leading the way to more adoption of LEDs as a lighting source.

LED Street Lighting