More than anything, I love early 70's FM radio. Marvin Gaye, Curtis Mayfield and Issac Hayes are easy examples to point out, but most of what I've heard, I've never been able to learn who it was (I have a lot of homework to do). All I can really say is that Chicago, Philadelphia and Detroit made some of the best music ever in '69-'74. Old school, pre-disco R&B rules.
Besides that, the first six Black Sabbath albums are the best blues albums ever recorded (even if they're not well recorded). Robert Johnson, Leadbelly, Jelly Roll Morton, Django Reinhardt, Charles Mingus, Nina Simone, Billie Holliday, Thelonious Monk, Charlie Parker, John Coltrane, Ella Fitzgerald, The Drifters, The Four Tops, The Beatles, The Doors, Jimi Hendrix, Pink Floyd, Frank Zappa (from the Mothers onward), Sonic Youth, Jane's Addiction, Misfits, Crass, Pixies, The Pogues, Bauhaus, The Cure, Crash Worship, Slayer, Brujeria, Neurosis, old Metallica, Sinead O'Connor, Belly, Erykah Badu, Bjork, a lot of 80's pop, and late 90's female R&B (girls like Aaliyah, Brandy and Monica were hot stuff).
I despise Eminem and most modern rap, but good hip-hop is amazing. NWA, Wu Tang, Roots, De La Soul, Beastie Boys, and anything else that used it's brain.
Finally, Wolfgang Amadeus Mozart and Gustav Mahler put all the rest to shame. I think they were the greatest inventors of music ever and music history owes them an incalculable debt. I also really like Rachmaninoff, Stravinsky and Debussy.