I was putzing around looking for a cheap rental for the weekend, I've booked through Hotwire in the past, but just going to southwest.com and booking through their site(easiest if your'e logged in) got me the best discount and some bonus miles to boot. Got a compact for $11.95/day before taxes/fees.

"From November 1, 2011 through May 31, 2012,, you can earn up to 2,400 Rapid Rewards Points and save up to 30% or more on qualifying Budget rentals. This offer is valid on all car groups at any participating Budget airport location in the United States.
Rent for 1 - 2 days and earn 600 points & save up to 30% or more
Rent for 3 – 7 days and earn 1,200 points & save up to 30% or more
Rent for 8+ days and earn 2,400 points & save up to 30% or more


For reservations, book online at southwest.com and enter coupon number MUAZ017 in the Coupon field to receive up to 2,400 points and enter BCD #U072700 in the Corporate/ID Rate field to receive up to 30% or more off your rental. Discounts greater than 30% may be available in certain markets. Be sure to provide your Rapid Rewards account number at the time of reservation or check in to receive your points."