I'd agree on doing something useful for the foundations aim. My suggestion would be to take an existing project aimed at kid friendly programming (Ao lice, etc), port it to the pi if necessary and then extend it to allow easy use of all the pis features - eg accelerated graphics and gpio pins. The other half of this is to develop materials and tutorials that could actually be useful to teachers and children. This may require actually talking to people and real user experience testing not just pure coding. I can guarantee you that a well rounded project with both real coding and softer real world skills will be a real benefit when applying for jobs.
According to the FAQ Computing At School (http://www.computingatschool.org.uk/
) are the people working on the official educational material for RPi and I'm certain they will welcome help and will have plenty of ideas in how you can best help!