Veronica the bat, Legend the cat, and Melisa the angel seedrian.
Fancharacters are extremely common in the Sonic fanverse, but it is quite unlikely that SEGA will take a fancharacter and put it in their games, but who knows? Maybe they're secretly being inspired by some good ones, and/or that they'll make a competition or something in the future...
The reason for this is that Sonic is one of the most famous video characters there is, his animal, yet slight human-like style makes it more interesting for fan-characters to be based on him, also Sonic's abilities usually encourage the creator of the fan-character to have their own story line and abilities.