Mario Kart 64
One of the most universally beloved games in Nintendo history, the original Mario Kart is still played by children and adults alike. And while you can still buy a new Mario Kart 64 cartridge for a moderately reasonably price, some eBay sellers are offering original print mint condition copies for over a thousand dollars. The highest-priced cartridge currently is listed at $2,500!
In the late 90s and early 2000s, HitClips were the coolest way to hear your favorite songs. Of course, the iPod quickly took over and made these little cartridges of music completely obsolete, but collectors will stay pay a surprisingly large amount of money for them. Some players even go for $100.