The Federal Firearms License 03 (FFL03)/C&R License allows you to become a licensed collector of Curio & Relic (C&R) firearms. This includes pretty much any firearm older than 50 years as well as certain special configuration and certain "oddity" weapons.
There are 11 types of FFL. The FFL03/C&R License is useful for anyone who is interested in purchasing surplus rifles and/or pistols. The fee for the C&R is $30 for three years. The benefit is that it allows you to purchase this type of weapon without doing an FFL transfer, which, in my area costs between $10 and $25 dollars, depending who you purchase from; so if you buy more than three collectors weapons in three years, the license is worth it. You need to keep a record of all of your transactions, but that's not a big deal.
The best resource for obtaining a C&R is the Surplusrifle.com FFL03 Curios & Relics: A Primer, I'm not going to repost everything they listed, since they already have the most complete reference. Following their directions, I received my C&R license in about one month. The only hard part about getting the license is finding your CLEO (Chief Law Enforcement Officer) information, which is fairly trivial; either Google for your area's Police Department (for me it was Fairfax County Police Department) or possibly call your county or city non-emergency number. If you call, ask for the name and business address of the Chief of Police for the purpose of obtaining an ATF Federal Firearms License.
When you want to start making purchases, you will need to send a signed copy of your FFL03 to the dealer. I keep a list of C&R dealers updated, whenever I find one, see my link in the references section (below). I highly recommend Southern Ohio Gun Distributors Inc; their customer service is excellent and their prices beat show prices any day of the week.
References (The ATF site is so slow, I can only assume it is hosted on a 56k modem.)