Sonic the Hedgehog CD

Super Sonic (lost build of cancelled Sega CD port of Sega Genesis platformer Sonic the Hedgehog 2; existence unconfirmed; 1992-1993) - The Lost Media Wiki

Sonic the Hedgehog (2006) - MobyGames

Neto - Hacking H.P. -> Roms hacks / Sonic Delta hacks -> Sonic Delta 40Mb

Sonic the Hedgehog (Video Game 1991) - IMDb

Translations - Sonic the Hedgehog

Sonic the Hedgehog 3 (Prototype)

Sonic the Hedgehog 3 Hacked Cartridge (Genesis), SomeOrdinaryGamers Wiki

Sonic The Hedgehog 3 untitled (Hack) Preview by Nocedk on DeviantArt

Sonic Classics

DF Retro: Sonic CD - under-appreciated but still brilliant today