If using "classic rock" as a genre: Van Halen. They rock my world.
If just talking about "old rock bands": Ozzy-era Black Sabbath is one of my favorite bands ever. Pink Floyd is on my goosebumps list as well.
I'm assuming that it means mainly older rock music. After all non of these bands were ever considered 'classic rock' when they were going, they were just rock or pop bands.
Black Sabbath are prob one of my favs, I got to see them when they did their reunion show at download fest and it was unbelievable. I got a free ticket too which makes that show even better for me. I wish I could have seen them in the early 70s when they were really tearing it up.