The Warren Ellis & Adi Granov complete reboot of the Iron Man story. Big ramifications in this volume with Extremis and Granov's design influence on the look of the Iron Man movie armor.
This is the core of the Iron Man universe, ranging from the Gene Colan & George Tuska era through the now considered classic David Michelinie/John Romita Jr./Bob Layton run all the way through to the end of the volume with Len Kaminski & Terry Kavanagh. Over 28 years of Iron Man history are in Volume I.