Thought might be interesting to anyone looking to break in to film/tv production sector. I personally have done a decent amount of ad-hoc work and it definitely helped me to get a full time job.

few websites to start:
http://www.lovestudentfilms.com/jobs
http://www.mandy.com
http://www.artsjobs.org.uk/
http://www.peopleperhour.com/

hope that helps