Here is an interesting idea: Create a Craig's List clone and run it on the Microsoft Azure Services cloud computing platform.

Craig's list is essentially an online classified ads system that I am sure everyone has seen. It has some problems though. I bet that I could make a "better craig's list" if I had a solid way to deploy the site in a global hosting environment. Enter Azure Services from Microsoft as the answer to that deployment question. Azure includes a full up Asp.net hosting platorm that includes WCF service hosting, a database system called SQL Data Services, and connection to the Microsoft Live Services for friends lists, IM, chat, and email. Everything could go in the cloud ... ads, images, text, buyer profiles, seller profiles ... all of it.

All you would have to do to make it better than the existing systems is to create a buyer/seller management application. So, sellers could see a list of all the ads they have posted and manage communications with the potential buyers through the site. Buyers could search for content and add "watches" to specific ads/auctions or for specific products/services. Make the management app have a super sweet UI with Silverlight and you have a winner.