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There's also an alternative that gives you the opportunity to develop directly for iPhone and iPad on Windows using Microsoft Visual C++.

Take a look at:

http://www.youtube.com/watch?v=e_I8MK8cfYI

For more information visit:

http://sio2interactive.com/SIO2_iPad_and_iPhone...

@RW: Thanks very much for an insightful, real world review of Unity3D.

I have used Unity3D Iphone for over 9 months. Here are the objective pros/cons.
Pros:
1. The editor is very good and meshes well with rapid prototyping design methodology.
2. The community is very helpful. Many useful snippets of code have been contributed to the public, and this will save you a lot of time. Some are critical (read GUIManager2) and would take months to recreate yourself.
3. You can script in 2 different scripting languages - Jave and C# (Boo is not supported for iPhone).
4. Because you are scripting and dealing with the engine at a high level, you won't get bogged down with low level details.

Cons:
1. You can't use SVN/CVS or any other version control software. Unity uses binaries that change constantly. So if you are going to work on a project with more than 1 person, you realistically have to buy their asset server. (They have been claiming for a long time they will make it work with SVN but selling their asset server is a revenue stream for them; don't expect it anytime soon).

This makes their costs deceptive when doing a price comparison. Until very recently you had to buy Unity Pro just to get the asset server even if you only wanted Unity Iphone (they are different). The total cost for all that came out to around $2k. So you think "oh it is just $300 bucks," but that is just the teaser to get you into the door.
2. You can't use the iPhone simulator. Unity writes instructions directly for the ARM processor. So the iphone simulator will not work. You will realistically need to test on an actual device.
3. #2 can also lead to problems when apple has a bug. For example, because of a bug with apple you can't compile Unity iPhone for an OS greater than 3.0. So if there is some feature in 3.1 or 3.2. You won't be able to use it.
4. Unity GameObjects have 2 initialization phases, Start and Awake, and their non-deterministic behavior can very subtly and harshly bite you in the ass if you don't know what you are doing.
5. If you script in C#, you will want to install parallels or its like to simultaneously run windows and Visual Studio C#. Mono is just not good enough. This means buying a windows license and parallels type software.

Overall the engine is is good. Time is money and you will probably get your game to market much faster than other engines. But you will pay more for this engine and its features.

Bork3D was just tested last night w/ iPad. After a two-line modification the engine runs flawlessly as a native iPad application.

Hi, We have Cocoas2D with developer and used that for one of game development and we get good result now we are developing same game with 3D in iPhone and using OpenGL and other - Thanks

Check out the Bork3D Game Engine, http://bork3d.com

There's also GameSalad. It's very simple to use and doesn't require that you know how to program.
www.gamesalad.com

Thanks for telling me about it Nestor, looks like it will be good once the release iPhone support.

Yeah, definitely depends on you, and what you're developing. I tried out the editor before, was excellent, and looks vastly improved now.

I do not have prolonged experience with unity3d, but I have had the trial for almost a week now and I am really enjoying it. I haven't yet decided if it is worth the $600 yet, but I am definitely thinking about it.