I'm not a helicopter man myself, but the Merlin is quite pretty, as is the Gazelle. My favourite aircraft are as follows:
TSR.2 (British nuclear bomber, cancelled before it went into production. Revolutionary, gorgeous.)

The de Havilland Sea Vixen. The best-looking jet fighter
ever, no contest. Shame about the Red Bull markings, but AFAIK this one is the only airworthy example left in the world.


Spitfire > everything else. Beauty incarnate.


Most modern aircraft are pretty soul-less in my opinion, however there are a few beauties to be found:
The unique SR-71 Blackbird, one of the few American aircraft I like:

The YF-23. The other modern American aircraft I like. I wish they'd chosen this 'un instead of the fugly F22...


There are a couple of gorgeous Soviet and British concept aircraft from the Cold War, but I can't find pictures of them (as I can't remember their names

).