Per country:
England: Hurricane (without it BoB would have been lost)
Germany: FW190 (short nosed versions, it just looks like a fighter)
US: P-47 (with the razorback, heavier than a fully loaded Do-17. )
Japan: Zero (1st long range fighter! With it Germany would have won BoB)
Russia: IL-2 (Sure it was cannonfodder but the sheer numbers built wow!)
As well as the Hurricane, I am a big fan of the Mosquito, especially since I found that I live about 3 miles from where it was designed and visited the museum on that site. If you're near St. Albans or Watford and want to see the Mossie prototype, let me just quickly plug the museum 8)
Anyway, apart from being a stunning aircraft visually, and a massive innovation in construction techniques, the Mossie showed massive ability as a bomber, night fighter, interdictor/strike aircraft, pathfinder, torpedo bomber, maritime patrol and photo recon type. The only thing that stopped the Mosquito/Hornet line from developing into a long-serving worldbeater was the advent of combat jets (a field de Havilland also dominated in the late 1940s/early50s).
The Avro Lancaster. BofB fighters have featured considerably in the messages but we must remember that the valiant fighters prevented the Luftwaffe from helping the enemy to prepare for an invasion. They could have regrouped and built up their numbers for another attempt later on. Bomber Command came into its own by attacking all kinds of munitions factories and workshops and carried a massive load at over 20,000 feet. The Lancaster was cold, uncomfortable and noisy but it was an airman's plane.