I’ve been trying to study the development API for iPhone for awhile now. I wasn’t able to find a good one until yesterday.
This one from iCodeBlog is very awesome! The author Brandon Trebitowski has written a very detail Introductory tutorial to iPhone development. I find it very useful!

Part one explains basic use of xCode and Interface Builder. He also demonstrated some basic game design framework.
Part two talks about user interactions.
Part three discusses about putting a Splash screen to an applicaiton.