Alison Doyle, a very knowledgeable blogger on job search and job sites has an excellent blog on job sites. She writes that "it's important for job seekers to know that they can find all the job listings they need without paying a dime." To back that up she provides a listing of free sites.
Her recommendations for analyzing a job site are especially useful. In short, don't pay for job postings or listings. If you're looking for a job, she's a primary resource.