I've been listening to classic rock as long as I've been alive thanks to my hippie parents. So as great as the Beatles, Stones, Who, Dead, Floyd and Moody Blues are they're off my list.
Elvis Costello - as the Barenaked Ladies said "I'm all about value" - so many good songs to listen to over 15-20 great CDs.
Richard Thompson - also making great music for close to 40 years now, also with a wide variety of styles, from his Fairport Convention days through the present
Tori Amos - daffy goddess of the piano (and harpsichord), also with a large catalog of good music (and and ever-growing catalog of not so good . . . )
Chris Whitley - a great guitarist and soulful vocalist, RIP.
Vivaldi - I'd probably find some 40-CD box set monster, even though my favorite performance is of his works for lute by Jakob Lindberg