January 26th in North America and January 29th in Europe for X-box 360 and PC to be exact. Of course as with most titles now the title will have a pre-order bonus, although only the North American bonuses have been announced. This includes some special ops armor and weaponry that boosts skills and abilities.
In North America GameStop’s Mass Effect 2 preorder bonus will have Terminus Assualt armor that can be used for extreme planetary conditions, increased running speed and personal shields, and augmenting weapons with an additional magazine of reserve ammo. GameStop’s preorders bonus will also include the M490 blackstorm heavy weapon which generates a high-powered localized gravity well and accelerates particles to near-infinite mass.
Also in North America if you preorder at any other retailer you get Inferno Armor which gives a negotiation bonus to Commander Shepard, an increase in running speed, and augmented damage from combat powers.