In Magic:The Gathering (a CCG), the Power Nine are nine very powerful, and out of print, cards. As such, they are really hard to find, and are all valued at close to $300 each. Like Dual Lands, they are Magic's equivalent of gold: always a solid investment.

They are:
Mox Ruby
Mox Jet
Mox Pearl
Mox Sapphire
Mox Emerald
Black Lotus
Time Walk
Ancestral Recall