Black Lotus
The absolute best card ever printed for Magic: The Gathering.

This card is so good that people today buy it for prices of AT LEAST $1000.00

This card is so good that cards that were specifically made to do exactly 1/3 of what it does (Lotus Petal) and cards that were specifically made to be insanely crappy versions of it (Lion's Eye Diamond) got banned along with it because they were abused just as much.
If you have a Black Lotus, DO NOT SELL IT!!! Wait a few decades (make sure to keep it in mint condition) and then sell it when its average Ebay price is about $5000.00+