Most of us know about the auto features: levels, color, contrast, but what if you want to take them to next level? Well, I found an article over at DaryaPino (summertomato) and she links to a great article over at the Digital Photography School website that explains Filters and Masks, and should help to get the ball rolling.
Here are some other links to check out as well:
How Can You Edit Photos on Your iPhone - Chris Pirillo
20 Best iPhone Photo & Video Applications - Brainz.org
61 iPhone Appls to Enhance, Edit, View and Share Your Photos - funkyspacemonkey
If you have any questions let me know :)
Digital Photography School