When I rent cars, I always try to rent hybrids. They're much better (or rather, much less worse) for the environment than normal cars.
The last time I rented one, I was at the rental car desk, and the representative slipped into his sales mode:
"Oh! I see you're renting a hybrid! You know, that's only one step below our highest class. I could upgrade you for FREE to an SUV!"
Um, is someone missing the point?