At least on Alaska Airlines, you avoid the federal taxes and fees on your ticket if you buy it in the next two days. See the site below:

http://www.alaskaair.com/content/travel-info/help/tax-reductions.aspx?wc_mid=1506%3A11695%3AWHA_AH_20110805_TaxRelief_PacNW&wc_rid=1-446DWKK&wc_lid=button_Save_Now_||20110805_AW||

Alaska is now my favorite air carrier and I use it a lot from Portland to Las Vegas. They also have flights to several east-coast cities and a number in the midwest.

http://www.alaskaair.com/content/route-map.aspx