Airline Pilot Central is very useful for looking up payrates for regionals, majors, freight carriers, and fractional operators. Each company's profile also lists when the most junior captain was hired, whether the carrier is currently hiring, and in many cases provides a link to the company's career website.
The International Air Transport Association, or IATA, is a worldwide organization of major passenger and freight airlines. You may find their member directory useful as a browsing list of major airline websites - although if you are looking for a specific airline, google will obviously be quicker.
The Regional Airline Association (RAA) is an organization comprised of mostly U.S. regional airlines as well as a good many charter and freight carriers. Their memberlist is extensive and comes in quite useful while jobsearching.
The National Business Aviation Association (NBAA) is a good place to look if you're interested in corporate, charter, or fractional work. Their "Director of Member Companies, Aircraft, and Personnel" is invaluable for anybody pounding the pavement in search of corporate gigs, but unfortunately is only available to member companies. You may be able to find a dog-eared copy at your local FBO. Otherwise, NBAA does have a Products and Services directory online. Corporate flight departments aren't listed, but there are quite a few charter and air ambulance ops, crew leasing / contract pilot businesses, aircraft ferry outfits, and training companies. A lot of these are niche players that you might otherwise never find.
Besides ClimbTo350, you can find job listings at FindAPilot, AvCrew, CorporatePilot.com, and others. There's a pretty good comprehensive list at ThirtyThousandFeet.com.