The photography enthusiasts at weblog Photojojo detail how to use a vintage manual-focus camera lens with your DSLR camera for a fraction of the cost of newer auto-focus lenses. There's not really much to it—just buy yourself an adaptor ring and go hunting for a vintage manual-focus lens on eBay and you're good to go. As an added bonus, it may even improve your photography:
Using manual focus on those old lenses will slow you down a little. Not too much, just enough to make you think about your shot. You feel more connected to your camera and to the process of shooting.
If you've ever given this a try, let's hear how it worked for you in the comments.