I found this site interesting. I knew there were rental places, but never knew what the prices were. I don't have a digital camera now, but if and when I do I would look up this site. Thanks!
Here's another to add to this listing. Also, most Calumet Photo locations have lens rentals. Usually Canon and Nikon, and usually autofocus, though some rental places will offer medium format, large format, or older manual focus gear.
I use to rent most of my gear when I was starting out in photography. Then I switched to mostly renting lighting gear. Finally I was making enough that I purchased and now own most of the gear I need, other than specialized grip and large lighting gear. Renting is a great way to maximize profits and try out gear prior to purchasing.
I've used lensrentals in the past and can highly recommend them. I've also heard great things about a few other internet lens rental places. Obviously only good for modern autofocus equipment but the customer service is top-notch.
For those in the Portland Oregon area, it should be noted that you can rent almost anything your heart desires at Prophoto. Including the $32,000 hassleblad digital back! Actually the biggest bargain there is rental of hassleblad 500EL kits.