Getting cheap airfares these days isn't so easy, especially if you live in North America.
Meanwhile budget airlines are booming elsewhere in the world. In Thailand for example, you can fly from Bangkok to Phuket for about 30 dollars on Air Asia, a relatively new budget airline. Of course in Europe, you have airlines like Ryanair that offer incredibly cheap airline tickets between many European cities. You can go from London to Paris for fifty bucks, as long as you don't mind having no preselected seats and a very strict weight limit.
Those types of discount airlines haven't really made it over to this side of the pond. Still, with companies like Jet Blue etc you can find some decent deals, especially if you buy plane tickets early; or take advantage of last minute deals. In Mexico recently we've seen companies like Azteca Airlines, Volaris, and Interjet attempt to replicate Ryanair type of budget service; with varying degrees of success. In Canada cheap flights are very hard to come by. There's basically nothing in the domestic market...internationally, Zoom Airlines has just started offering cheap flights to Europe. Otherwise you may get lucky if you're traveling when a charter is.
With the web, shopping for air fares is easy. There are many companies selling plane tickets on the internet. From the comfort of your chair you can surf many different web sites until you find the best fare possible. This is power that only travel agents had just a few years ago!
Carefully check out exchange and refund policies - sites like Expedia for instance are known to be quite strict in that area. Most online air ticket sales use E-tickets - typically the company that sells you the tickets just emails it to you. Print it, bring it to the airport and have a safe and stress-free trip!