Shepard's new Geth Plasma Shotgun and Phalanx heavy pistol.
The pack arms Shepard with the 'Phalanx heavy pistol,' which developer BioWare says "hits like a hand cannon but features increased precision," the semi-automatic 'Mattock' rifle and the triple-barrelled 'Geth Plasma Shotgun,' which "allows users to charge up each shot for increased damage or just blast away rapid-fire style." Splendid.
The Firepower Pack is available for download now on PC and Xbox 360 at the price of $2 (160 Microsoft Points, 160 BioWare Points). A story-based DLC pack titled 'Lair of the Shadow Broker' is currently in the works, teaming up Shepard up with Liara again.