Mashups are applications which combine data from 2 or more distinct web services into a single application. All 7 of the AWS services are excellent raw materials for mashups, of course.
The Web 2.0 Mashup Matrix is a great way to find interesting mashups. You could also use it to find new opportunities -- a pair (or more) of services that have yet to be combined. Finally, you can track new mashups at MashupFeed.
If you haven't had enough mashing, you can also try to attend Mashup Camp.
Update: How could I forget the Web 2.0 Innovation Map?