A little more underground than some of the other toys on this list, Magic: The Gathering certainly isn't any less valuable as a result. Magic was one of the first trading card games to exist and it's still popular today, having moved to an online platform. The game is a sort of battle between wizards and is based on a fantasy world. The high value of the cards today makes sense, as anything remotely 'fantasy' themed tends to sell for a lot of money once it's considered vintage.
Launched back in 1993, you wouldn't think a simple deck of cards would be worth so much. But an Alpha Starter Deck (still in the original packaging) will sell for $8,000 to $9,000. A black Lotus Alpha Deck is worth a crazy $27,000, as there were only 1,100 ever printed.