A few common ones are described in July/August edition of RCI Endless Vacation magazine:

AY - aviation security surcharge
Used for airport screening, sky marshalls, security training
$2.50 each flight leg, $10 limit per round trip

XF - passenger facility charge
Used for airport improvement projects
$4.50 per takeoff, $18 limit per round trip

US - domestic passenger ticket tax
Used for US aviation trust fund (FAA)
7.5% before taxes

ZP - domestic flight segment fee
Used for US aviation trust fund
$3 per leg