I have gotten a number of gigs off of Craigslist, but I also check boards for jobs in specific fields (there are boards for zookeeper jobs and boards for journalist jobs for example) so you should figure out if there are any of those that would be relevant.
I have found Monster to be useless. I have a couple of those things set up where Monster emails me jobs that are supposedly relevant to my resume, which I can't turn off because I can't remember my password, and they are never useful, but this is obviously because of my specific preferences - Monster jobs always seem to be at huge corporations and that is not my thing.
I did once have someone contact me because they saw my resume online either at Monster or the Washington Post job ads site - they both have functions where you can upload your resume and make it searchable to people. I got an interesting tour of some animal labs out of it, and if I had been desperate for full time work at that point, I would have followed up. That's the only thing that ever came of those sites for me. It's probably worth doing since it's not a huge investment of effort.
But, and I am sorry to say this - what they say about networking being critical, it is unfortunately true. If I sat down and listed all the jobs and all the freelance gigs I have ever gotten, I am pretty sure that more than half of them had something to do with knowing someone. Quite a few were jobs that were never listed anywhere. Either someone asked their friends and colleagues if they knew someone who was looking for a job like this, or it was somewhere where I already knew people directly and they asked me. Others were jobs that were listed, but I am pretty sure I got the interview, or got the editor's attention or whatever, because I knew someone who knew someone.
So, you need to make sure people know you are looking, even people who you might not think are relevant to a job search - I got a good article assignment once because my next door neighbor knew an editor.