Until the end of 2013 (not 2012), you will earn 7,500 Club Carlson miles for a 3-day Avis rental. Most parts of the world participate, but please take careful note of the geographic restrictions and black-out dates listed in the small print.
6,000 Club Carlson points gets you 750 Avios. 8,000 gets you 1,000 Avios (and you could send some American Express Membership Rewards points across to top them off, at 1:3).
This is, admittedly, not a lot more generous than crediting to Iberia (300 Avios per day) but it gives you extra flexibility. Club Carlson partners with over 20 airlines, not just Avios. And, of course, you could also redeem your points for hotel stays if you did multiple rentals.
This won’t suit many people, but if you do a lot of 3-day car rentals then it might be worth focussing on this deal throughout 2013.