Check out FlyBe's baggage charges. This European discount carrier charges next to nothing for fares, but oh do they sock it to you with the baggage. They might as well be in the freight forwarding business.
Get this: they allow only 10 KG (that's about 22 pounds) in carryon luggage (that's free, for now anyway); then each checked bag costs $24, but it can weigh no more than 20 KG (that's about 42 pounds) before excess charges kick in. And those excess charges? $18 (about 9 pounds UK) per kilo (that's 2.2 pounds), or about $9 per pound.
So if your bag weighs 20 pounds over the 42 pound checked bag limit, you'd pay $180 each way plus the $24 base fee, or $408 round-trip!
With the strict and low carryon weight allowance, they basically force you to check your bags.
So before you buy that cheap ticket on a foreign "discount" airline, be sure to get the facts on their baggage fees.