A friend of mine released a nice app for the iPhone which will notify you of new apps as well as allow you to set strike points for desired price levels for specific apps. The kist of planned features was quite long and it would really be a much better interface than the actual App Store app on the iPhone. When you click "buy" it of course takes you to the actual Apple App for the purchase.

I haven't checked it out since the early releases, so I'm not sure how far he is at this point. The program is called AppSniper and should also be available as a free release.