Avis is offering 2500 bonus Delta miles on a 3-day rental and 5000 bonus Delta miles on a 4-day rental. You must use the relevant coupon codes mentioned in the link in order to get the bonus.
It’s offered on “a qualifying rental at participating Avis airport locations in the contiguous United States and Canada.” Qualifying presumably means paid, i.e. no free day coupons in conjunction with the bonus mile offer. And airport Avis locations only.
The terms and conditions do not specify any maximum number of times that this bonus can be earned, and important point in light of the recent imposition of a limit on the number of times you could earn the Delta bonus from Budget (which is owned by the same company as Avis). Although even there reports are that folks are actually receiving their full bonus miles.
This is a worthwhile offer on longer rentals. For single day rentals I still prefer crediting to Virgin Atlantic which offers 1000 miles.
I do have some upcoming rentals already booked which will qualify. There is a report on Flyertalk where adding the coupon code online bumped up the rate, but that adding it over the phone did not. So I may have to make a phone call, something I rather hate doing (I’m just not a telephone kinda guy).