I spent this past weekend shooting in NYC with some lenses I rented from a few different websites, and I found myself super pleased with the results. I used both Borrow Lenses (for a 50mm 1.4) and Lens Rentals (for a 10-18mm). The process was equally painless for both sites and I'll definitely be using them again. Check them out if you get a chance.
Nikon 50mm 1.4
Canon 10-18mm