The Microsoft Accessibility Labs is sponsoring the W4A Web Accessibility Challenge at the Web 4 All conference in Beijing, April 21-22, 2008.. This contest is open to anyone who has a practical solution for a Web Accessibility issue. You don't have to be a researcher or work for a software company. All you need  is a good idea that's built and working.  Submissions require a short video demonstrating your idea, a 2-page abstract, and attendance at the conference. They're due on Monday, at 12:00 a.m. (midnight) Hawaii Standard Time (HST).
Here's a short description of the challenge, from the W4A site:
This year, the second "Web accessibility challenge" aims to gather innovative accessibility technologies for rich Internet applications, collaboration services, collective intelligence systems, real-time collaboration systems, location aware systems, multilingual Web sites, local language input methods, and other systems invented for globalization.
All the details can be found at W4A Web Accessibility Challenge Sponsored by Microsoft.
Deadline too soon?  If you're a student, you may also want to consider the Imagine Cup Interface Design Accessibility Award.  Submissions for this Microsoft sponsored event will be accepted until May 2, 2008.