OK, so I'll admit that most of the apps I have on my iPhone are of the "stupid" variety. The favorite of my stupid apps is the one that makes my iPhone turn into this really cool Star Wars lightsaber -- will all the cool sounds -- and as you wave it around in the air, it makes those "crashing" sounds like you're having a real lightsaber fight with a Sith Lord (or your choice of protagonists or antagonists).
But some of the iPhone apps I have are incredibly useful. One such example is Color Expert, which was created by the folks at Code-Line Software, the same folks who create Art Files (a collect for output plugin for Illustrator), and Sneak Peek Pro (a QuickLook plugin which allows you to preview Illustrator and InDesign files in the Finder in Leopard), as well as several other cool apps.
Color Expert ($9.99 from the iTunes App Store) is kinda like Adobe Kuler for your iPhone, but it's better in my opinion because of its full integrated Pantone Library support (including the new GOE colors). You can create color themes by spinning a color wheel and choosing colors. You can also get instant color conversion that include LAB, RGB, CMYK, HSB, and PANTONE.
You might ask why you'd want to create color themes on your phone instead of on your computer, but the reality is that as a designer, we're inspired by things all around us -- not only when we're planted in front of our glowing computer screen. For example, I was walking with the kids in a nearby park and was struck by the sheer beauty of some of the swans in the water. And here in NY (and much of the east coast for that matter), this time of year is famous for foliage that turns from summer green to fantastic colors of fiery orange and red. And so on. Once you generate a color theme, you can email it to yourself or to others.
What's cool is that Color Expert is hooked up to the iPhone's camera. Snap a photo, click on a region of the photo and instantly find the nearest Pantone color. Then generate a palette of colors to match. It's perfect for when you're shopping for an outfit and you want to match a pair of shoes or a scarf. It's color inspiration... anywhere.