There are plenty of iPhone themes out there for Android, but not all of them are very good. Some of them rely on you buying a home launcher application as well, which leaves you out in the cold.
Well there is one such app that I have been using for over a year now, and I am simply in love with it !
Espier Launcher is a free download for Android 1.5 and up. Below are few screenshot I took from my mobile.
I hope your search for an Iphone theme for android ends here :) Cheers !
Update : This app also got featured in one of the articles at lifehacker.com : Espier Launcher Makes Your Android Phone Look Just Like iOS