BargainBin [Free - iTunes link] keeps an eye on App Store apps and lets you know about sales and price drops. So, if there's an app out there you're waiting to try, but are watching your budget, this might be a way to keep track of any discounts coming your way. With push notification, you'll also know quickly when to pounce on the right deal.

If you give it a try, let us know how it works for you!