Chase has an iPhone app that lets you deposit your checks by taking pictures of the front/back of the check, and submitting it through your app on your iPhone. I've already been using this for a couple months now, and every time I make a deposit like this, I'm always amazed. Just spectacular.
Star Gazer is another one. The interface is great, and you can search for a constellation, planet or star, and it uses arrows on your iPhone to direct you to it.
Shazam is an obvious one, but still amazing. It pretty much works every time for me, almost anywhere.
There is an App that lets me remotely access my PC from anywhere using my iPhone; I also sometimes connect my laptop to my HDTV, and can use my iPhone as a media controller and a wireless mouse.
I guess I probably sound like an iPhone fan boy, but you probably would be too if you had one.