Id consider the Diamond and the Omnia. Understand that these devices use Windows Mobile, therefore you will probably find you need to use the stylus from time to time. The diamond has an internal stylus to the device, whereas the Omnia doesnt. Also, if you can wait, check out the HTC Touch HD as its looking like a sexy piece of kit.
My only warning would be to try one before buying. The O/S is a lot more complicated than that of the IPhone, however its got full freedom of the device and you can tweak it as you see fit. Persoally I prefer my Diamond over the Iphone by miles, but I dont mind fiddly software, adn having proper bluetooth is very handy, as is being able to use the device as a portable drive.