I also use this one. It simulates an analog meter with fancy sound effects that can by annoying. The Fotometer Pro app is pretty good. Don't know if it's the best.
http://itunes.apple.com/us/app/fotom...439913393?mt=8

Pocket Light Meter will save your reading as a photo with f/stop and shutter speeds with GPS coordinates too. The price is right with this one. It's FREE.