The App Exchange allows you to subscribe to an RSS feed for apps submitted into a specific category. There is an XML link on the left-hand side of the category page to do this.
I tweaked the URL from one of these and made a feed for getting every submission across all categories. You have to include, but leave blank, the Category parameter. Then you have to set a length. The default Salesforce uses is 20. I set mine to 1000 so that I got a download of all the apps up there so far.
The link above will take you to the one I am subscribing too. You might want to knock down the length variable. There were 162 submissions that I received when I added the feed to my reader.