I always seem to write about The Immortal Sun, but the pure power level of the card is through the roof for any creature-based deck
Fetchlands This may be an obvious choice but I think the Onslaught fetchlands are important not only for Modern and Legacy, but also for Standard
They claimed rewriting all the spell descriptions according to formula would prove impossible because hundreds of spells would need templating in 48 hours to meet their delivery deadline
Its more than just a game
Olle Rade and I used to play so much Vintage with each other at Pro Tours, and both of us were fond of Fastbond, particularly when the printing of Wasteland made the format into a giant joke
However, you do have access to some of the best artifact removal in the game which, when paired with Liquimetal Torque, can also become much more flexible