Alright, I admit that it's not all "classic rock" but I am way too huge of a Dream Theater fan to leave some of their stuff off.
1.Scenes from a Memory - This album tells a super compelling story while still hitting some of the best of rock, ballads, and acoustic has to offer.
2.Six Degrees of Inner Turbulence - Another album that is a rollercoaster. Orchestral openings and closings around some fantastic and thought provoking rock and acoustic awesomeness
I'll move past Dream Theater so that it's not too much of an overload, but overall, their lineup is great. Also check out "Black Clouds and Silver Linings" as well as "Systematic Chaos" by them.
Rush - 2112
Rush - Moving Pictures
Kansas - Leftoverture
Kansas - Point of Know Return
Jean Luc Ponty - Enigmatic Ocean
Alan Parson's Project - Tales of Mystery and Imagination
There are my two cents of some of my favorite albums from some of my favorite bands. I love albums that tell a story and that flow naturally from one song into the next.