Screens from early versions of the game showed different colours on the HUD.

Ryu originally had different art at the select screen. The "PLAYER SELECT" text was also coloured blue.

Here are a bunch of unused sounds from all three SF III games.

SF III: New Generation

Announcer: "Gill Wins"
The only way this could be heard would be in a 2 player vs match. But as there is no code to unlock Gill, this goes unused.

Jingle Bells theme
This most likely would have been used in the location test build of the game, which had Christmas and New Year related messages for the player. It goes unused in the final game however. The location test messages can be found in one of the SFIII Japanese guide books:

SF III: 2nd Impact

Akuma: "Gouzanku"
I tried doing every move Akuma has, but I never got him to say this.

Unused female fighter sounds?
I found these all lumped next to each other in the sound test. I don't think they are used but if anyone knows different, tell me.

SF III 3rd Strike

Announcer: "You need to practice more"
It might be possible that this clip and the one above it were intended to be used in the bonus games.

Announcer: "Super Art ready"
In the actual game, whenever you fill up your super art bar, the announcer will say "Alright let's go!" instead.

Alex: "I'm Ready"

Gill: "I am your God"
This is not used in the arcade version, but in the console versions, you can hear him say this by beating the first bonus stage.

Gill: "Witness my life eternal!"

Ken: "Shippu Jinrai Kyaku!"
This should be used with Ken's third super art, but it isn't. He just makes a load of grunts whenever he performs it.

Urien: "You've got no chance"

Twelve: "Shinryuken!"
The deal with this is that Twelve has a super art where he can transform into his opponent and can use any of their normal and special moves. Whenever he does a special move, his voice sounds weird with this garbling effect going on. For example, this is what Ken's Hadoken sounds like, this is was it sounds like when Twelve does it. However, checking in the sound test reveals that all the super arts have this effect recorded for them too! Perhaps Capcom originally intended the transformed Twelve to be able to use super arts?