I think it's safe to say that there are very few, and perhaps not any, rock guitarists who've used the instrument to as many ends as Queen's Brian May. Over the course of his career, he's experimented with all sorts of overdubbing techniques in his famed guitar orchestrations; used delay to extensive effect (particularly on "Brighton Rock" on both live and studio versions); arranged all sorts of accompaniments in countless styles; and played some of the most beautiful (and varied) solos ever recorded. He strikes me as part George Harrison (i.e. he puts the the band first and thinks like a session musician) and part Clapton (i.e. he can wail). I also think that working with Freddie Mercury must have pushed his abilities a great deal, as frequently Mercury would be quite precise in what he wanted from the guitar, but because he would use the piano to demonstrate, May would then be required to find ways of playing parts that were not in the standard bag of rock guitar tricks. Of course, he made large contributions to Mercury's development, and to the other members' as well. If I had to pick one track as representative of May's six-string artistry, it would be "Death On Two Legs", the opening track from A Night at the Opera (1975). Every note that he plays is brilliant, but the sound sculpture guitar solo is amazing, even by his standards: http://www.youtube.com/watch?v=v4zmv1IFCOA.