I've got a blackberry, so my options are limited in that arena (there is no RunKeeper or CardioTrainer or a lot of the other apps for BB). Plus, it's a company phone so I can't get any pay apps on it.
The Nike+ says it's 90% accurate out of the box and improves with calibration. So far, that looks true. As long as it's within a quarter mile or so that's probably ok for my purposes unless I start getting way more serious about my runs.