The iPhone. Now that my wife has one, I can really see why Apple turned the mobile phone market upside down.
The device really is a good product. The touch screen is absolutely light years ahead of anything HTC has put out, and the OS that it runs is worlds better than Windows Mobile.
I just have one problem with the devices, and that is iTunes. Apple's iTunes is quite possibly the most annoying, bloated, resource-hogging excuse for a media player.
In addition, I have had to reset the iPhone configuration once, losing all of the apps that were installed on the phone. I can re-download these and not pay any more (since they are already tied to the account), but there is no clear way to re-download all of the apps that were on the phone without going one-by-one. This may not be the worst thing in the world, but it certainly is annoying.
-Steve