My list of WWII American aircraft (so I'm not saying it's my be-all, end-all of greatest planes period):
1. F4U-4 - Best American fighter of the war, if not the best all-around Allied fighter period. Sorry Pony fans.
2. C-47 - Workhorse transport and cargo plane. Couldn't have won the war without it.
3. SBD Dauntless - Sunk more enemy tonnage in the Pacific than any other aircraft, and was second only to the submarine in total tonnage sunk.
4. F4F Wildcat - She may have been out-performed by the P-38, F4U and F6F, and out-classed by her chief adversaries, but it was the Wildcat that saw the Americans through Coral Sea and Midway. Japan had enough experienced pilots after Midway to recover in aircrews, if not warships, but they could never recover from the losses suffered at Guadalcanal. And it was the Wildcat that drove that nail into the coffin.
5. B-24 Liberator - The B-17 may be more famous, but the Liberator was the workhorse of the bomber fleets.