Sonic hentai stands for adult artwork in any form (mostly drawn images), involving the characters from the video game "Sonic the Hedgehog".
Many Sonic fans do not seem to approve that type of artwork but there seems to be also many of them who do not care.
Known sonic hentai artists are Kio, Toyjo, BbmBbf, Zeta R-02 and the list is growing as the game becomes more popular and there is more demand for sonic hentai.
Aku Toyjo is said to have quit drawing sonic hentai because of his art being stolen but there are some hints that show that he takes commissions and stays in the background.
Most of the artists' works can be easily found with a Google search.
Also a Sonic hentai doujinshi (comix) called Furry Bomb exists that is the most popular comic along with Sonic XXX Project from BbmBbf.
Current Furry Bomb issues are 1, 2.5 and 3 where there is known of a new rare 4th issue.
Finally there is a sonic hentai game under development called Amy Xtreme Adventure from Kio and expected to be released next year(2007) along with his new website.
Pink haired cute female hedgehog that made her first appearance in Sonic CD, where she is captured by Dr. Eggman and Sonic sets off on an adventure to rescue her.
After Sonic CD she only made her appearance in Sonic Drift, Sonic R and Sonic the Fighters until Sonic Adventure, in which she was a fully playable character and had a completely new modern hairstyle.
The games she participated so far are:
Sonic CD, Sonic Drift, Sonic R, Sonic the Fighters, Sonic Adventure, Sonic Adventure 2 Battle, Sonic Heroes, Sonic Advance 1-3, Sonic Riders. (Also in the Sonic X episodes)
Amy pursues and wants to marry Sonic, but he ignores her and leaves alone all the time, however she doesn't give up.