Jaheira, Friend of the Forest turns all your tokens into Moss Diamonds and Llanowar Elves, at least in terms of mana generation
While Cavern of Souls feels like the biggest hit in the main set, Im also very excited about Growing Rites of Itlimoc and Resplendent Angel because these cards have crept up a lot in price over time
Almost every ally creature in Magic: The Gathering has an effect that buffs every other ally, gets better the more allies are on the battlefield, or triggers when more allies come into play
Wrong Back or Mixed Cards Every now and then, sheets from different games get mixed up at the factory, leading to legendary oddities like a Pokmon card printed with a Magic back
Titania, Protector of Argoth is a popular card and commander, and putting more of folks favorite (non-broken) cards into the field is good for us all
Uncommons are the siren of the casual designer because thats where we tend to feel its okay to push something we like a lot, as long as we can justify it as being a bit bad in some way