I have a long list of axis aircraft. From the top of my head:
Messerschmitt Bf 109Z
Messerschmitt P 1101
Junkers Ju 248
Junkers-Argus attack aircraft (or the EF 126)
Focke Wulf P III or P IV
Focke Wulf P VI (aka Flitzer)
Arado Ar 240C or Ar 440
Lippisch P 20 (turbojet Komet)
Henschel Hs 123 (again)
Henschel Hs 132
Dornier Do 26 (as a long-range recon with Hohenthwiel)
Dornier Do 435
Focke Achgelis Fa 284 (flying crane)
Fiat G.56
Ambrosini SAI.403
Caproni Ca.331! (my absolute favourite!)
Savoia Marchetti SM.91
Fiat AS.14
CANT Z.1018 Leone
and a whole bunch of Jap fighters and the Ohka rocket version.
Kris
There were several I still haven't explained. So in short:
Messerschmitt Bf 109Z
A twin Bf 109 much like the Twin Mustang. I think it would have been an excellent stop gap aircraft as it required very little time to develop and no new production needed. The Bf 109Z would have been an excellent Zerstörer, faster than the P-51 and armed with up to 5 30mm cannons. I also think it could have been used as an escort fighter, a reconaissance fighter, a fighter bomber and a anti-Mosquito nightfighter. So within a few months it could have been used instead of the much more expensive Me 410, until the Me 262 would have been ready ('45).
Messerschmitt P 1101
Many people talk about the Focke Wulf Ta 183 although the P 1101 was quite similar but was actually built. It would have been built with non-adjustable wings and with the new HeS 011 engine. It would have been the best fighter on earth, superior to the P-80, Me 262, Meteor or Vampire.
Plus, it would have been easy to build.
Junkers Ju 248
aka Me 263. Basically a Me 163 with a double endurance. Was easy to build, easy to fly and with R4M rockets it would have been an excellent point interceptor, for instance in the Ruhr area.
Focke Wulf P III or P IV
I don't think the Me 262 was really what the Germans needed: it was complicated, expensive and needed two engines. Germany could not hope to compete with the industry of the allies. That's why I strongly believe in the Volksjäger program which asked for a cheap and simple single jet engined fighter. Of course it shouldn't have been used by the Hitlerjugend but by regular fighter pilots. One could build two or three Volksjäger for the price of one Me 262.
Now, the Volksjäger program was started in (IIRC) September 1944 when it was way too late. So I think it should have started a year earlier. There were few single jet engined fighter designs: the Messerschmitt P 1108, the Lippisch P.20, ... and the Focke Wulf P III (or P IV, the name is uncertain). I prefer the latter because it has the engine on top - so it wouldn't suck up objects on the grass airstrips - and had straight wings which were essential for rapid pilot schooling.
Focke Wulf P VI (aka Flitzer)
I like this one because it looks so much like the British De Havilland Vampire. That also makes me believe it was a succesful design even though it never flew.
Arado Ar 240C or Ar 440
The improved Ar 240. The Ar 240 was a remarkably fast aircraft, unlike the Me 210 and 410. But it was also unstable. This seemed to have been remedied by the later Arado designs but by then the Me 410 was already in service. Yet, the Ar 240C would have been an excellent night fighter and long-range reconaissance aircraft. I don't see much catching this Ar 240C.
Lippisch P 20 (turbojet Komet)
Already mentioned this one with the P III and P IV. The Me 163 was a delight to fly but the problem was its short endurance. The P 20 was like a Me 163 with a turbojet engine. Was also very simply to build and heavily armed. So this too could have been excellent Volksjäger interceptor.
Henschel Hs 123 (again)
I love this little aircraft and find it's a pity that it wasn't put back in production. Would have been excellent against partisans and for night nuisance missions but could also be used for daytime missions as they were more manoeuvrable than the Stuka or Hs 129 for dodging enemy fighters.
Henschel Hs 132
The well known turbojet dive bomber. Finally a successor to the Stuka (at least as a dive bomber) and excellent for attacks on specific targets (bridges, depots, rail junctions, ...) and naval targets.
Dornier Do 26
Perhaps the most beautiful seaplane ever (aka the Seeadler). It was designed as a transatlantic post and VIP aircraft but because of its great range I think it could have been excellent as a maritime reconaissance aircraft. It would have been used instead of the Fw 200 and Ju 290 because it also had the advantage of landing at sea, where it could be refuelled by U-boats as it had diesel engines. On the other hand, it could also supply U-boats (post, spare parts, wounded people).
Dornier Do 435/535
This is the night fighter version and the mixed propulsion version of the Do 335. The Do 435 had a side-by-side cockpit and would have been an excellent night fighter because of its high speed and good endurance. Also as an intruder, outclassing the Mosquito. The Do 535 had a jet engine in the back, and this might have made it a better fighter and especially an escort fighter. Would have been great to see this patrolling the seas or attacking targets far away.
Focke Achgelis Fa 284 (flying crane)
The Fa 223 is better known but had a limited carrying capacity. With a BMW 801 engine the Fa 284 could have carried 7 tons. This would have given the Germans a fantastic tactical weapon as it could suddenly fly in heavy weapons and halftracks to difficult terrain or to mountainous areas. Especially in the mountains it could fly in supplies in a few hours where else it would have taken days. Especially interesting because the Germans were often fighting in mountainous terrain.
Kris