Another guy that no one ever thinks of as a great quarterback is Warren Moon. He's third all-time in passing yardage and fifth all-time in touchdowns.
He didn't do enough in the postseason. He only got those stats because he stayed around forever.
Moon's stats were put up in fewer games than anyone else ahead of him on the list. In fact, of all the top ten quarterbacks in passing, completions, and TDs, only Joe Montana played in fewer games than Warren Moon.
Remember, Moon spent six years of his prime in the CFL. Of course, you can't count his stats there, but if you did, he would be far and away the top completion, yardage and TD guy of all time. Even without those years, he's still in the top five in all those categories.
The post-season knock is made against a lot of quarterbacks, but I don't think it sticks as much against Moon. He led the Edmonton Eskimos to five Grey Cup championships, proving he could get it done in the post-season. Houston was the Indianapolis Colts of the late 80's/early 90's, with Moon puting up monster numbers, but never having the defense that could win a Super Bowl.
Last, but not least, Warren Moon was one of the first black quarterbacks in the league, and its first successful one. With that came a lot of pressure and scrutiny that many others folded under. He proved that a black man COULD be a NFL quarterback, and opened the door for many of today's stars like Vick, McNabb, and Cullpepper.
All things consider, I believe Warren Moon to be one of the top five or six quarterbacks of all time, certainly better than most of the guys on this list. I think it's a real shame he doesn't get the recognition he deserves.