Sonic 1 - Green Hill, Spring Yard
Sonic 2 - Oil Ocean, Metropolis
Sonic 3 - Hydrocity, Launch Base
S & K - Death Egg
Spinball - Toxic Caves, Lava Powerhouse
Sonic 3D - Gene Gadget (Saturn version)
Adventure - Be Cool, Be Wild and Be Groovy, Run Through The Speed Highway, Red Hot Skull, Mechanical Resonance
Adventure 2 - The Supernatural, Space Trip Steps, Unstable World, Highway In The Sky, Won't Stop, Just Go!, A Ghost's Pumpkin Soup, Rhythm and Balance, Scramble For The Core, For True Story... really the whole OST, it's a masterpiece
Heroes - Bullet Station, Hang Castle, Mystic Mansion, Egg Fleet, Robot Carnival/Storm, What I'm Made Of
Shadow - Westopolis, Lethal Highway, Central City, The ARK, GUN Fortress, Black Comet, both GUN battle remixes
06 - Flame Core, Crisis City
Secret Rings - Let The Speed Mend It, Seven Rings in Hand
Unleashed - Rooftop Run day, Cool Edge day, Arid Sands both
Colors - Tropical Resort 1 & 3, Planet Wisp 1, Asteroid Coaster all
Generations - For True Story remix, Rooftop Run Classic
I have quite an extensive Sonic playlist on my player. I've even looped a bunch of the songs out to 7-9 minutes apiece to listen to them longer.