Quoting Planeman, here's the unabashed and, above all, CORRECT list of 10 greatest bombers of all time!
As the numbers of actual strategic bomber designs which actually saw use was so low, I've included some tactical bombers as well if they were really important.
What's the number one may be discussed - but this is The Definitive List!
1.) Gotha G - Forced Brits to keep a significant portion of their manpower, AA and fighters to defend London. Besides, it's the coolest looking of them all in a steampunk (or should I say, petrolpunk?) kind of way
2.) B-47: The workforce of SAC when the SAC was the truly important part of US military. B-47 was the plane which forced Soviet Union to use gargantuous amounts of money for PVO.
3.) B-29: Served as design study for Tu-4, the most important Soviet bomber. Construction of Tu-4 forced the US to use gargantuous amounts of money for US continental air defense. Tu-4 was the most feared Soviet bomber, regardless of it's actual capabilities. B-29 also had a kind of effect in Japanese-US unpleasantness.
4.) B-17: The plane which broke Luftwaffe's back. Not by itself, but because of it there were a load of P-51's flying to Germany destroying Luftwaffe's fighters. Also forced Germans to use a load of resources for their air defense.
5.) Super Etendard. Exocet-carrying Super Etendards of Argentine Navy had a disproportionate effect on British Task Force operations during the Falklands War. Were used also for strategic missions during Iraq-Iran war.
6.) F-16. Combat debut destroying Osirak, extremely important in almost all post-Cold War conflicts, still forming the backbone of many Air Forces. Most recent strategic bombing mission made just few weeks ago. It has F designation, sure, but for most of it's life it's been pounding dirt.
7.) B-2. It has showed that even non-nuclear bombers can have strategic effect. A British politician said "Bomber will always get through", but this is the plane which actually reaches this specification.
8.) SBD Dauntless. If sinking most of the Japanese carriers wasn't strategic, then what was?
9.) B-25 Mitchell. Made the most important strategic bombing mission of WW II, the Doolittle raid
10.) Fairey Swordfish - Devastated surface fleets, supply transports as well as the Italian Navy