I've seen a few requests around the internets for an app store RSS feed. Until Apple releases their own, I have stumbled upon a useful one:
feed://webobjects.mdimension.com/iPhoneApps.rss
Enjoy!
[robg adds: I discovered (thanks to TUAW) a number of App Store feeds provided by Pinch Media:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080714205935422