Well, we've got Megaman and Metroid, why not Sonic.
Sonic The Hedgehog: Green Hill Zone
Sonic 2: I can't pick one...I just can't. I love EVERY song in this game....EVERY SINGLE ONE (Sonic 2, next to some NES games a few years back, was my first game ever, along with Aladdin =D)
Sonic 3: Ice Cap Zone Act 2
Sonic & Knuckles: Lava Reef Zone Act 1
Sonic Spinball:Toxic Plant (It's the first level, I can't remember what it's called)
Sonic CD (US)- Stardust Speedway (Bad Future)
Sonic CD (Japan and Europe)- Stardust Speedway (Good Future), Metallic Madness (Present)....I love a lot of the songs in this version, it's too hard to pick one!
Sonic 3D Blast (Saturn)- Puppet Panic Zone Act 2
Sonic 3D Blast (Genesis)- Puppet Panic Zone Act 1
Sonic R- Super Sonic Racing (Song)
Dr. Robotnik's Mean Bean Machine- The game music (I have no idea what to call this one >.>, it's when you actually PLAY the game, you know?)
Sonic Adventure- Main Theme (I forget what it's called, it's when you fight Chaos as Super Sonic)
Sonic Adventure 2- Live and Learn