http://steveweller.com/articles/toolbar-icons/
[Note: I have created a companion article that covers tab bar icons. It includes an updated template with new guides and a new example project.]
Creating good-looking iPhone toolbar icons is definitely a challenge. The background must be transparent and the icon antialiased. It's also white, so you'd like to work in white against a dark background and have some sort of preview that you can reference. Unless you're a Photoshop or Illustrator jockey, it's hard to know where to start.
I create pixel-perfect icons for my iPhone apps using OmniGraffle, a toolbar icon template, and a simple workflow. You can buy OmniGraffle from Omni Group and get the rest here. Note that although I'm creating a bit-mapped PNG as the final output, I'm working with vector images. This gives me the freedom to adjust and tweak as needed for the best output.
Download the template. It contains an OmniGraffle 5.1 document and an example Xcode project that uses the UIToolbarItem icon.
