I've used Lens Rentals.com and like them.
For me, the best part is the fact that they don't charge a deposit. I was in NYC and was going to rent a lens from, if I recall, B&H. They wanted a deposit to cover the full value of the lens. My current rating, thanks to a spiteful ex-wife, doesn't permit me to have a credit line to cover that. With Lens Rentals (and Borrow Lenses.com) that's not a concern. They don't charge a deposit.
They ship it to me door, and it arrives the day I need it to arrive. Shipping may or may not be pricey, depending on personal opinion, but I think they're a great service.