Hertz is offering 3,000 Virgin Atlantic miles per rental through September 30th. You have to use their rate code to get the offer, which may not be the best rate available, but 3000 miles is a good offer nonetheless.
(I usually rent from Avis and take advantage of their standard 1000 Virgin miles per rental, most of my rentals are for just a single day or a couple days, and rack up the Virgin miles quite nicely, thank you.)