Black Sabbath - Embryo/Children of the Grave
Not that I really consider them 'classic rock' but Guns N' Roses is my absolute favorite band of all time. It's almost a shame that most people know them for 'Welcome to the Jungle', 'Sweet Child O Mine' and 'Paradise City', when in fact their best songs are the ones most people haven't heard. 'Coma' and 'Estranged' are some of the best pieces of music I've ever heard, by anyone, and almost everything on Chinese Democracy was overlooked because Slash wasn't on it - do yourself a favour, check out 'Sorry' and 'Prostitute'.
Aerosmith and Motley Crue were the first 'big' bands I ever saw on the Route Of All Evil tour in 2006, and both bands were pretty important to me when I was younger, and they still are.
Good stuff so far!