http://aws.amazon.com/startupchallenge-final-event/

It is always good to pay attention to the innovators around us. Some of the applications listed in the AWS final can be used by affiliates. One of the sites is even an affiliate themselves with some pretty creative programming (although currently a bit buggy.) There are "free" tiers on a few of the services. One is for facebook, another for mobile.

If you are inclined, check Google for finalists from previous years also. Over the past few years, I have found a few nice apps, including Animoto - a nice video tool.