Expenditure is another great-looking app found via the excellent Well-Placed Pixels blog. It's an expense tracker -- you can add transactions into the app with just a few taps (and even attach a photo, note, or category to each debit or credit), and then browse your collected budget. Obviously, you could use it to just see how much you're spending each month, but it can also be used for things like traveling (the app will automatically calculate currencies for you) or keeping track of business expenses. It's not a super full-featured business application, but it will do the basics smoothly and beautifully.
You can find it on the App Store for US$1.99, and as an iTunes commenter points out, using it will probably save you the $2 you spend on it. There is a lite version that only allows eight transactions (enough to see the app in action, though not enough to actually put it to use), so if you're not sure about spending a couple of bucks, you can check it out that way as well. Excellent app -- the functionality is a little limited (by design -- the developers just wanted a simple expense tracker), but the great aesthetic and design elements make up for the simplicity.