Careerbuilder, Monster, ComputerJobs (for IT), Dice (for IT), and yes, now LinkedIn. I personally haven't been on the job-hunt in about 4 years, but when I was, the first four at least were one I used. I didn't get onboard with LinkedIn until after I was already in my current job so I can't fully speak to that.
And as suggested previously, if you have a particular company in mind check their web site. That would be the best, most direct route to take. Most of the listings on the job sites above are posted by "headhunters" and could start out as contracting jobs rather than an immediate direct hire. Especially IT jobs.