MSNBC have done an article on the 10 most obnoxious hidden airline fees, I have summarized their list below or you can read their article at the below URL:
1. Making a reservation on the phone or in person
Fee: $5-$20. US Airways is among the greediest on this count: $10 to book over the phone, or $20 to book at the airport or at a city ticket office (if you can find one).
2. Re-banking frequent flyer miles
Fee: $50-100. If you cash in your miles and decide not to use your ticket, you’ll be hit with a fee to place the miles back into your account.
3. Cashing in frequent flyer miles without sufficient advance notice
Fee: $0-100. Who says frequent flyer tickets are free?
4. Bringing a pet onboard in the cabin
Fee: $50-85 (each way). These fees have skyrocketed lately
5. Checking luggage
Fee: $3-10 (each way). We’re talking here just about checking even one bag
6. Getting a refund when a fare goes downFee: $25 to $200 or more. If you bought a TV from Costco or BestBuy and they lowered the price the following week, chances are you could get a refund, no questions asked. Even Apple gave credits when it dropped the price of its iPhone soon after launching it.
7. Flying standby on the same day of travel
Fee: $0-50. Time was, if there were empty seats on a later or earlier flight on the same day as your original, the airline would confirm you for free. But now, most airlines charge to take an earlier or later flight on the same day as your original flight
8. Paying for lap children
Fee: $10 to 10 percent of the adult fare (international flights).
9. Getting a seat assignment
Fee: $5-$11 each way. Air Canada, AirTran and Allegiant
10. Using the lavatory
Fee: OK, airlines are not installing pay toilets. Yet. But the way things are going …