Stuff I can't find in iTunes...
 

Bumming me out considerably:

No Herb Alpert w/ or w/o the Tijuana Brass
No The Smiths
No Wall of Voodoo
No Cocteau Twins
No Robin Trower from 70s
No Black Sabbath before 1980
No Frank Marino
No Al Stewart
No Herman's Hermits
No Fun Factory
No Marty Robbins

There's a lot more missing than this but I can't remember the other things I came up empty on.

To be fair, tho, there is a lot of stuff in iTunes that I didn't expect to find. Leading the "I can't believe they have this one" list is this song that's been in my head since I was 7:

The Cowsills: The Rain, the Park and Other Things

I would like to take a moment to formally compliment you on your taste in classic popular music.