A while back I mentioned that I wanted to read Ed Brubaker's (still ongoing) run on Captain America. Well, I'm also interested in reading some previous runs of Captain America...
Silver Age Captain America - Collected in four volumes of Marvel Masterworks. I've got the Essentials v1 but I would prefer to read them in color. Classic stories that introduce classic villains and organizations such as M.O.D.O.K. and A.I.M. The last volume includes the first appearance of the Falcon. The second volume seems to be currently out of print.
Jack Kirby's return to Captain America - collected in three volumes: Madbomb, Bicentennial Battles, The Swine.
The Invaders - link - Tales of Cap and other superheroes (Sub-Mariner, Original Human Torch, Union Jack, Spitfire, etc.) fighting the Nazis. I read and collected some of this series back in the early 80s. There are currently three collections: v1, v2, v3.