Here's an offer that's been around for a while, but worth a repost. United Mileage Plus Elite members who rent from Hertz through February 28, 2010 will earn 2,000 bonus miles for
full size or larger vehicles rented 1-4 days in length, and 4,000 miles for each rental 5 days or longer. The bonus is in addition to the 50 or so miles Hertz awards for a standard rental.
Click here for full details.