I was about to say May's 'Brighton Rock.'
maybe it was just the order i heard things in, but that solo redefined what rock guitar was for me in a lot of ways.
"Brighton Rock" might be his best solo, but you have to give honorable mention to his arrangement on "The Millionaire Waltz." For those that don't know, it does to guitars what "Bohemian Rhapsody" does to vocals. Great tune, great orchestra.
Oh, and honorable mention has to go to "Good Company" for making guitars sound like woodwinds and brass...