I used Joe Hewitt's excellent iUI library as the base, although hacked it quite extensively. Also, prototype.js is always a time saver.

The hardest part about the iPhone app, I felt, was just reducing clutter.

Theres a series of articles on A List Apart: http://www.alistapart.com/articles/putyourcontentinmypocket

Also check out iui, which makes getting an iPhone site up and running real easy and fast.