Good idea, Doug - and I can tell you from experience, it works very well.
As some of you may know, I run a boating site -
The C-Brats for C-Dory owners. Throughout the years, many of the participants there have done the same thing, albeit on their own. We supply the site logo to anyone interested, and any of a number of online places will whip them up cheap. Vistaprint.com is a popular choice...they almost always have a special going where one can get 250 cards for $10 or so.
We've gained tons of new members from handing out these cards to curious folks met on the road/water.