One of the best ways to decide if you want to purchase a lens is to rent it first. Additionally, some photographers will so rarely use a speciality lens that it doesn’t make sense to do anything BUT rent.
The problem is, unless you live in a very large city, you probably don’t have a camera store that rents lenses near you.
Now you can rent lenses online. Several companies specialize in this service. A company called Rentglass.com and ships rental lenses for Nikon and Canon cameras anywhere in the Lower 48 states. It rents up to 300mm on the Nikon side and 400mm on the Canon side. It also rents some camera bodies and flashes.
The company carries a broad range of glass up to 400mm f/5.6 L.
Another company to look at is http://www.lensrentals.com/. They also rent lenses, camera bodies, tripods and flashes. They seem to have a larger range of gear for rent, including super telephoto lenses. In addition to Nikon and Canon lenses, they also rent Tamron, Tokina, Sigma and Sony lenses.
The third and final company on my list of lens rental houses is called http://www.webelenses.com/. They only rent Canon gear.
Most of these companies rent lenses for periods of one to three weeks at prices, including 2-way shipping. You arrange the rental online; transit days are not counted against your rental period; and the optics are shipped in a re-usable box with a prepaid return shipping label included.
I am not endorsing ANY of these companies since I have never used them. If you have used them and have an opinion as to the quality of their lenses or service, please leave it in the comments section.