Another online travel site to consider is: kayak.com. It's worthwhile to look for cheap fares on these sites. Once you narrow down an airline though, it's often worthwhile to go directly to the airline's website and book the fares from there. They're about $5 to $10 cheaper on the airline website.

If your in Europe try Ryanair.com Super cheap. About 10 euros for one ways tickets. The catch.....Super ghetto. No reserved seating, first come first serve and some people wait about 3 hours+ to get a cheap flight. But a lot of locals use this airline so its not too bad. You make up in savings!!!

ANother good site to look at is farecast.com. they have an interesting additional feature, whereby they number crunch trends to predict for you whether they think an airfare is likely to go up or down closer to the date of travel, thereby assisting you in deciding when best to book. Also - apparently mondays are also a typically cheaper day to book travel according to some guides I've read

This is a pretty good video - most suggestions are good but everyone has another discount carrier that has a cheaper fare. Farecast and kayak are normally about the same as most other discounters - the best thing to do is to google discount airfare and try as many of the discounters as you can stand.

We just discovered vayama.com Cool site for international trips. Try the 3D seat map.

vayama.com is a really good site for international trips. Never found a website that is so easy to use. Highly recomended.

another good site is skybus.com :) this was very useful! :)

This is very American-centric, although I suppose you have many non-US viewers… In Europe as well as Ryanair mentioned above (in my opinion and experience, a very nasty company) there is Easyjet which has real fares ( I use them often) from about 5 euros (plus airport taxes) from, say, London to other European capitals. They tend to use smaller airports well outside the capitals, but still, it's cheap. You more or less have to book online, best is way ahead or be very flexible. Major carriers NEVER discount here, though of course they have cheap fares if you book ahead.

good luck with this economy