There are so many job sites and newsletters available online that the biggest challenge is just sorting through them. Here are three that I've found to be useful:
freelancewritingjobs MORNING COFFEE newsletter - fresh freelance jobs delivered every Tuesday morning. Completely SPAM free.
Get Copywriting Jobs newsletter/site - Visit their site and you'll be automatically invited to sign up for the newsletter. There is a little bit of SPAM here, in the form of rare promotional messages and offers from the folks that run the newsletter - but there are also lots of job leads to be had.
Now I have to admit that I lied. The second site is of no use to me because I'm not a copywriter. But if I were...