AppSniper for the iPhone and iPod Touch Video Review
I'm on a quest to (eventually) have a blog post about how the iPhone can pay for itself in saving you time/money. Since today's app merely helps you save money on more apps for the phone, I suppose it doesn't count, but it does allow you to add more apps for free, rather than paying for them.
AppSniper tracks prices in the App Store, and shows you how the price of specific apps is trending over time. It also gives you a list of previously pay apps that are currently free, and also app that are reduced in price. See an app you want but it's a little too expensive? You can set a sniper watch on it, set the price you'd like to pay, then the app will notify you when the app drops to that price. AppSniper quickly pays for itself, and there aren't a ton of apps that can't make that claim.
Here's a look: