Karametra, God of Harvests helps you to build your mana pool in creature-focused decks
The company was bragging about producing counterfeit Magic cards, claiming them to be their hottest-selling product
Promos from early events can be strong too
Me, the Immortal #147 Doctor Who Change Version Me, the Immortal Legendary Creature Human Rogue At the beginning of combat on your turn, put your choice of a +1/+1, first strike, vigilance, or menace counter on Me, the Immortal
Certain foil basic lands can also be worth a shocking amount, especially those which feature foiling on top of the old-style card frame a combination which was only present for a couple of years at the turn of the millennium
: Add X mana of any one color, where X is the amount of life you gained this turn