Story: "Superboy 1,000,000: OMAC One Million And Counting!" (23 Pages)

Credits:

Karl Kesel (plot, script, inks)
Tom Grummett (pencils)
Comicraft (letters)
Buzz Setzer (colors)
Mike McAvennie (edits)

Feature Character:

Superboy One Million (the One Millionth Actual Clone of Superboy; last in Young Justice #1,000,000; next in DC One Million #4)

Guest Stars:

Superboy
Superman of the 853rd century (last in Superman: The Man of Steel #1,000,000; next in Superman Vol. 2 #1,000,000)
Guardian II (a future timeline incarnation)

Supporting Characters:

Guardian II
Dubbilex
Mickey Cannon
Adam Winterbourne
Serling Roquette
Millionex (first appearance; a D.N.Alien of the 853rd century)

Villains:

Dabney Donovan (last in Adventures of Superman #562)
Solaris
Vandal Savage (both behind the scenes)

Other Characters:

Superboy 8-2-0
Superboy 3-5-4-1, other Superboy clones (first appearance of all; members of the Justice League "S")