Here are a few resources I found:

Good first intro http://mobile.tutsplus.com/tutorials/mobile-design-tutorials...

_plus's suggestion for designthencode.com was great

This was good to play around with layouts http://www.teehanlax.com/blog/iphone-gui-psd-v4/

This could be good http://www.tapptics.com/series/code-custom-graphics-xcode/