Don't fall for the Ryanair nonsense. They have appalling service, and dump you in airports miles from the place you actually want to go to (eg Frankfurt Hahn, 45 miles from Frankfurt in the middle of nowhere). You can get great deals on normal professional airlines (and get miles) without having to use Ryanair, which is often more expensive. If you want to disregard this advice, check out flybudget.com for more info about budget airlines and where they fly.