Here are some before and after pics using the Best Camera iPhone app by Chase Jarvis on some of my old iPhone photos. This seems to be a pretty nice simple post processing app that can sweeten iPhone photos without transferring them to your computer. Doesn't go too far with the effects like most do and you have the ability to modify the various filters in a non-destructive way...well, at least it's non-destructive before you save it.
I wish there was more control over highlights and shadows since some of these have gotten more blown out than I'd like, but in general, this app does a pretty good job. Not surprising since this was developed by a photographer.
Thanks, @holleyimage for letting me know about this.