Duke Nukem & Sonic Adventure.

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

Sonic The Hedgehog.

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

Trouble Shooter / Battle Mania.

http://www.sega-16.com/2011/01/lists-of-fury-10-best-genesis-easter-eggs/

http://www.youtube.com/watch?v=pgVz8dDHzzk

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 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

Jet Set Radio (Jet Grind Radio).

http://www.amazon.co.uk/Sega-Jet-Set-Radio/dp/B00004XQWB

Sega.

http://www.youtube.com/watch?&v=WV-6JhzLTuA

Source.

Sonic.

Source 1

Source 2

Sega and Sony.

Source 1

Source 2

Sonic Adventure.

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