Maverick Legacy
Maverick is a GW Legacy deck that can compete with blue decks in the format on library manipulation to always have the cards it wants, which is unusual for those colors.
Every now and then, green or white gets a powerful tutor of some kind, and when you get to add the best of them from throughout history, it creates a powerful package.
Green Sun's Zenith, Knight of the Reliquary, Stoneforge Mystic, and Garruk Relentless each allow the Maverick player to search for different things, and Sylvan Library offers a huge amount of card selection to a deck that shuffles so much.
Of course, being able to find any cards in your deck only matters if you can find cards that do the right things, and Maverick definitely has a wide variety of powerful interactions to search up.
Most of the time, the goal is to use Mother of Runes to protect another important creature: if it's Knight of the Reliquary, this will often involve finding a string of Wastelands; if its Stoneforge Mystic, hitting the opponent with a equipped creature; and if it's Thalia or Gaddock Teeg, slowing the opponent down or crippling his or her function.
Despite the deck's power, consistency, and practical game plan, Maverick, once a dominant Legacy staple, as been widely considered dead for some time now. Terminus was the first big problem for the deck, and adding Deathrite Shaman to the format made Knight of the Reliquary much weaker.
This weekend, Jack Wang used this deck to win the StarCityGames.com Legacy Open, accurately predicting a time when WU Miracles, the premier Terminus deck, would not show up or perform well.
Aside from merely reminding us that Maverick is still a powerful deck, I'd cite this as evidence that you should always keep old Legacy decks in mind—especially decks you've been very familiar with—to look for an opening to dust them off again when the metagame shifts to become more favorable.