There is one company I know of and have rented from: Fox Rent-a-car. Here's a link to their site:

www.evrental.com

I rented a 2006 Civic Hybrid out of San Diego and dropped it off in Phoenix back in April. It's not the cheapest rental you'll find, but at least you'll get a feel for the car and you will save gas money, which will offset some of the extra cost, compared to a non hybrid.