He's been gone a long time, and come October 14, 2009...
That's right, the X-Men oldest and greatest foe, Magneto returns in October to the pages of Uncanny X-Men. They are keeping things very tight lipped as to what will be going on, but issue 516 will be the first part of the seven part storyline entitled, NATION X.
No word as to whether or not this will tie into the current Dark Reign storyline that is encompassing the Marvel Universe. Or whether or not Magneto will break Norman Osborn's neck. (seriously, can someone do that, quick?)
Uncanny X-Men #516 is written by Matt Fraction with pencils by Greg Land (yeah, I know)