Well yeah, there was a plane. But maybe more than one.
Caught these articles over at Signs-of-the-Times:
"New study from Pilots for 9-11 Truth: No Boeing 757 hit the Pentagon"
And then of course, there's that curious story about Norman Mineta:
Norman Mineta sticks to his story: Cheney in White House bunker before Pentagon hit on 9-11, "Of course the orders still stand".
UPDATE: From Conspiracy Planet: Pentagon Eyewitness: Official 9/11 Legend Exposed
"(Samuel D.) Danner, a civilian pilot and electrical engineer from Hagerstown, Maryland, has recently come forward and told American Free Press that he saw an aircraft that resembled a Global Hawk making a tight turn at high speed before leveling off near ground level and smashing into the Pentagon."