Like others have wisely said, whats beautiful to you is what counts, and everybody has their own sense of style, well except maybe my friend Paul who, well, thats another story, but, my vote for most beautiful knife goes for something like this double action Dake folder. Its a good thing i own it, or id be jealous!
Or, here's a checkered black pearl Corbit, i dont own it, but think its awfully nice...
And one more, also WISH i owned it... Checkered mammoth ivory, inlaid rubies, great damascus, by Bill Pease.
Now, i would say all of these knives qualify as beautiful, but, as always, its in the eye of the beholder...