There have been so many fees lately, it's hard to keep track. It started with the fuel surcharges. Then the checked bag fee, which seems to have spread like a rash. Yesterday, American Airlines became the latest major carrier to charge passengers for checking a second bag. The fee: $25. United, Continental, Northwest and Delta all charge a similar fee. So far, Southwest appears to be a hold-out, but don't expect that to last. And then there's the ticket-change fee that United hiked by 50 bucks last week to offset rising fuel costs.