The guys and gals at ThinkGeek just sent me one of the coolest toys I've gotten so far this year. The Retro-Duo takes the internals from both Nintendo's original NES, and those of a Super NES to allow you to pull out your old carts and give them new life.
Since most modern TV's have made the old 75ohm connectors we used to attach cable boxes to disapear, the output boards allow for composite (Yellow video, Red and White audio) or S-Video output. I had to hunt through bins at 3 different Goodwill stores to find games (my NES stuff went bye-bye a LONG time ago), but was able to turn up Ice Hockey and Golf to give it a spin last night. When you can find them, carts are a lot cheaper now than they used to be. I got both games for $6.00.
My son and I had a blast (after I was forced to explain that these were actually good graphics when I was 10 years old). It took him a while to get used to the strange controls, but we had a couple of good games. I beat him, of course, but it was still some nice father-son time.