Essential iPhone GUI PSD
This is certainly old news, since I’ve known of it for quite a while—I typically hear things a bit late. I referenced it recently and was surprised no one knew about it. Joshua Corliss, the motion wizard over at AgencyNet, tweeted the third version earlier today and I figured it’d only help others to share the wealth. So, if you’re involved in iPhone design or development of any kind, this PSD is a must-have. Enjoy.
[update] – Kevin Suttle pointed me to Teehan+Lax’s Palm Pre GUI PSD. Check it out as well.

If you’re just looking to quickly wireframe an iPhone app, then the online verison of Balsamiq mockups actually offers built in iPhone widgets. It’s a pretty nice Flex app.
http://balsamiq.com/demos/mockups/Mockups.html
You can’t imagine how may PSDs like that I downloaded during the last two years.
@Matthews:
Balsamiq rules!
Especially in conjunction with the new Napkee (dot com).
Also, have you seen these yet!?
http://www.MockupMagnets.com
Awesome tool, just to get the ideas solidified with your team/client before using software for the details.
-E