I love [Oil-Gorger Troll]. ONE was one of my favorite draft environments, and I really loved the oil counter mechanic. I keep a very jank oil based edh deck around. He won me a bunch of games in draft, I love the art, and the "flavor" text (get it?) cracks me up.
The art, the solid mana cost and the frame colors make it an aesthetically very pleasing card, but when it was revealed I figured it would be a good draft card but not playable in Standard. But it turned out to be a fantastic stabilizing card in Esper Hero and punched way above its weight as an uncommon. GRN/RNA was also just a great era for Standard so it's tied to good memories from that time as well.
I'll always have fond memories of [[Aurochs Herd]]. I know a lot of people don't like Coldsnap draft, but I'll play it anytime, and I'll probably try to force green.
Once Upon a Time is perhaps the greatest gameplay-flavor integration win Magic has ever had. For a while, standard matches all began with someone saying the name of the card.
The most metal White card. Black gets all the cool spooky business, Red gets all the fury and devastation, and here's a goddamn nuke with minimal centered text.