Updating this old list with a few changes. A lot has happened in the Unity 3D community since I created this list: a basic Unity 3D is now free for Mac development, and DiamondTearz blog is no more, but has been changed to another site known as InfiniteUnity3D
Official Unity Resources – This is a wide collection of Unity iPhone resources including tutorials, sample projects, and the like. The Unity 3D people have really done a great job putting all this together. It’s really second to none when you look at the resources available for other iPhone game engines. The place to start is the videos. I think this is a great example of what other engine/game creators should try to put together.
Infinite Unity 3D – This is a terrific resource, the creator who ran the DiamondTearz blog previously has now created this site exclusively for helping Unity 3D users.
UnifyCommunity Wiki – A great wiki that is a tremendous resource for those developing with Unity 3D.
Those are the most helpful resources that I’ve found for dealing with the Unity iPhone game engine, as I said the documentation/examples are extensive on the Unity 3D site so you will want to start with those, but it can be great to find other perspectives.
The engine has also made great strides since their initial iPhone release so if you didn’t like it initially (there were some performance issues that seem to have been alleviated) you will probably want to check into it again as it has really become the market leader for 3D game creation tools on the iPhone. The iPhone version offers a free trial.