Palettes is a great app that allows you to create color schemes.
CliqCliq allows you to find the exact colors you wish to use and immediately converts them to a variety of scales and formats.
ZeptoPad is a sketch pad tool for your iPhone.
Caliper is a nifty measuring tool that like its names states uses caliper like jaws to measure objects.
Photobucket allows you to upload all of your photos to Photobucket and share them with your colleagues or clients all through your phone.