I'm bogged down in research right now, so I don't know that I'll have time to try any creative exercises in the foreseeable future, but I always like to collect them.
One idea I've had good success with for character development is to have the students take the Myers Brigg personality test...not as themselves but as characters they are trying to create. They then use the personality profile generated by the test as a reference in writing a character sketch.
On our campus the Career Resource Center offers the test. There are also a number of personality tests available online.
The students always enjoy doing this and maybe become a little too interested in personality types, but it does help them brainstorm characters.