Avis welcomes Southwest Airlines’ Rapid Rewards Members with TRIPLE credits and up to 25% off!
I usually don't qualify for these promos due to the terms - like a 5 day rental.

Terms:

Avis has joined Southwest Airlines’ Rapid Rewards as a preferred partner. From now until August 15, 2008, you can receive triple credits and save up to 25% off on a weekly rental of 5 or more days. For triple credits, you will receive 1.5 credits per qualifying rental. Valid on all car groups at any participating Avis airport location in the United States.

* Rentals must be picked up by August 15, 2008.
* An advance reservation is required.
* To get this discount, enter code K024700 at time of reservation in the "Corporate ID/Rate" field on southwest.com.
* Requires a minimum five-day rental period.
* If you are a Rapid Rewards Member, be sure to present your account number at the time of rental to receive Rapid Rewards credit.
* Offer does not apply to one-way rentals.