George Olshevsky was able to corral a number of great artists* to provide the covers for his Marvel Comics Index series in the 1970s. Neal Adams drew this nifty cover to issue #3, which featured the Avengers, Defenders, and Captain Marvel.
On this cover, my favorite Avenger, the Vision, is featured front and center. The Scarlet Witch is providing cover over him and Captain Marvel is taking care of the rear guard. All three characters were featured prominently in the classic Kree-Skrull war arc that Adams illustrated in the Avengers. The only Defenders representative is Valkyrie hacking away on the right. Adams really did a great job with all these characters.
*Editor's Note: Check out Steranko's Cover to the Marvel Comics Index, Nuff said!
Update: Comments from my old MT blog...