Duke U challenges students to improve Duke life using tech. $5000 in rewards.

It has two stages: (1) for prototype submissions and small prizes of ~$1,000, (2) final fully-working submissions and big prize of up to $10,000.

We entered the competition in 2011 with a book exchange site and won ~3,000. The site's still running.

Past winners: http://icampusprize.mit.edu/past-winners/

Edit: fixed wrong link