Two popped into my mind, and I'll list them chronologically.

1. The last panel of Amazing Spider-Man #18 ("The End of Spider-Man"), when he pulls his costume out of the trash can, puts it back on, and realizes, "I was born to be Spider-Man."

2. The last page of the last issue of Green Lantern/Green Arrow (#89), when GL destroys Carol Ferris' pollution-spewing nine-million dollar aircraft and tells her to "Send me a bill."