Primal Power
Primal Power is one in a series of class-focused supplement books released by Wizards of the Coast for Dungeons & Dragons 4th Edition. As the name says, the book is all about expanding options for the Primal classes of the 2nd Player's Handbook - Barbarian, Druid, Shaman, and Warden - in the form of new powers, variant class features, Paragon Paths, Epic Destinies, feats, and other miscellaneous goods. Equivalent books for the other sources were Arcane Power, Divine Power, Martial Power and Psionic Power.
Sadly, due to coming out before the third Player's Handbook, and Essentials killing off the X Power line, no bonus material was ever produced for the Seeker, save an article or two in Dragon Magazine.