Try the following Sonic CD cheats from the "Press Start" screen:
Down, Down, Down, Left, Right, Space - Sound test
Right, Right, Up, Up, Down, Space - High scores
Up, Down, Down, Lelf, Right, Space - Level select
Type in the following as "Time Attack Times":
25:46:12 - View all movies.
30:21:05 - Stage select menu.
37:27:57 - Plays music.
Press Up, Down, Down, Left, Right, [Space] at the title screen.
You can choose any past, present, or future level to play.
However, when you warp or finish the level you will return
to the title screen.
Development team high scores:
Press Right, Right, Up, Up, Down, [Space] at the title screen.