Airfare drops but you already have the ticket ?

US Airlines refund policy when you buy non-refundable tickets and the fares drop before departure.

AirTran: No refund
Alaska Airlines: Voucher with no change fee
American Airlines: Voucher minus change fee
Continental Airlines: Voucher minus change fee
Delta Airlines: Voucher minus change fee
Frontier: No refund
Hawaiian Airlines: Voucher minus change fee
JetBlue: Voucher with no change fee
Midwest Airlines: Voucher with no change fee if consumer requests refund within 7 days of buying ticket; otherwise, a change fee applies
Northwest Airlines: Voucher minus change fee
Southwest Airlines: Cash refund with no change fee
Spirit Airlines: No refund
United Airlines: Voucher with no change fee
US Airways: Voucher minus change fee
Virgin America: No refund