Sonic The Hedgehog 3.

http://www.vgfacts.com/trivia/605/

Duke Nukem & Sonic Adventure.

http://www.imdb.com/character/ch0008433/#game

Sonic The Hedgehog.

http://www.youtube.com/watch?v=6D9h-4vQUHM

Sonic 3.

http://www.gamesetwatch.com/2006/03/michael_jacksons_secret_sonic.php

http://www.mtv.com/news/articles/1627664/did-michael-jackson-compose-sonic-hedgehog-3-soundtrack.jhtml

Sonic Adventure 2.

http://info.sonicretro.org/City_Escape#Trivia

Update: Despite what the evidence suggested, Jaleel has just gone on record saying he was not approached by SEGA to voice Sonic.

https://twitter.com/jaleelwhite/status/290321104411705345

Sonic Generations.

Video interview where SEGA employee Aaron Webber states it was “either Jaleel or no voice at all”.

http://www.youtube.com/watch?v=Kt6w7og5UMk&t=2m9s

Article where Stephen Totilo states (after talking to Webber about Sonic Generations) “Sega couldn’t get him [Jaleel White].”

http://kotaku.com/5846911/sonic-will-meet-sonic-in-sonic-generations-and-other-amusing-revelations

Sonic Adventure and PaRappa the Rapper.

http://www.imdb.com/name/nm1393617/

http://www.youtube.com/watch?&v=GM8h2Xyis9M

Sonic the Hedgehog 3.

http://info.sonicretro.org/Knuckles_the_Echidna#Miscellaneous

Found another site saying the crescent was inspired by the Nike logo: http://bit.ly/ZZSDLU

Sonic.

Source 1

Source 2

Sonic Adventure.

http://tcrf.net/Sonic_Adventure#.3F.3F.3F