John W.R. Taylor wrote an introduction to one of his many encyclopaedias and in it he estimated that there were 35,000 different aircraft.
That was 1978.
And that was before the microlight/ultralight/kit aircraft boom - my estimate would be closer to 50,000 now. Regardless of that, we've got a pretty much endless list of aircraft, even if we (as we tend to) ignore the more common ones!