There are a plethora of job posting sites available online; however, keep in mind that less than 10% of landed jobs are the result of solely responding to a published opening. You must incorporate leads with networking. Ideally, you want to be introduced to an opening BEFORE it is posted.
Most companies post openings on their own company websites, pulling candidates directly into their applicant tracking systems. Third party websites are targeted to specific sectors, industries, functions or geographies making them more appealing to recruiters. The mega-sites (i.e., monster.com, careerbuilder.com) contain a broad range of jobs which produce enormous pools of applicants making it cumbersome for recruiters. Be certain to optimize the use of job postings in your search by setting job alerts on targeted job boards.