Norman Osborn art in the 616 Marvel continuity, pre-Dark Reign (listed by publication date)

Steve Ditko
Panels selected from (left to right): 
1.  Amazing Spider-Man #26 (July 1965)(unofficial appearance)
2.  Amazing Spider-Man #37 (June 1966)
3.  Amazing Spider-Man #37 (June 1966)
4.  Amazing Spider-Man #37 (June 1966)
*It's worth noting that Ditko provided two other 'unofficial' Norman Osborn appearances in both Amazing Spider-Man #23 and #27 as well*

John Romita Sr.

Gil Kane
Panels selected from (left to right): 
1.  Amazing Spider-Man #96 (May 1971)
2.  Amazing Spider-Man #96 (May 1971)
3.  Amazing Spider-Man #121 (June 1973)

Ross Andru
Panel selected from Amazing Spider-Man #145 (June 1975)(flashback)

Tom Morgan and James Fry (Romita Sr. provided additional finishes)
Panel selected from Amazing Spider-Man #274 (Mar 1986)(apparition)

Sal Buscema
4.  Spectacular Spider-Man Annual #14 (1994)(flashback)

Guang Yap
Both panels selected from Web of Spider-Man Annual #7 (1991)(flashback)

Aaron Lopresti
Panel selected from Amazing Spider-Man #365 (Aug 1992)(flashback)

Alex Ross
Panel selected from Marvels #4 (Apr 1994)

Bob Wakelin
5.  Sensational Spider-Man #32 (Oct 1998)

Sean Chen
Steve Lieber
Panel selected from Penance Relentless #4 (Feb 2008)

Brian Denham

Billy Tan
Panel selected from Thunderbolts #124 (Nov 2008)

Paco Medina
Panel selected from Deadpool (V2) #3 (Dec 2008)

Francesco Mattina
Panel selected from Thunderbolts #126 (Jan 2009)

Roberto De La Torre
Panel selected from Thunderbolts #126 (Jan 2009)

Mike Mckone
Panel selected from Amazing Spider-Man #581 (Feb 2009)(flashback)

Dale Eaglesham
Panel selected from Amazing Spider-Man Extra #3 (May 2009)(flashback)

Mike Choi
Panel selected from Fusion #1 (May 2009)

Tyler Kirkham
Panels selected from (left to right):
1.  Fusion #2 (June 2009)
2.  Fusion #3 (July 2009)