A lot, here are some links you might like :) http://sonic2online.com (Online games of sonic the hedgehog) http://www.sonicfangameshq.com/games.html (different download-able fan games)
Other than the extra abilities in several games like Sonic Unleashed, or Sonic Colors, Sonic doesn't 'gain' powers. He always had his famous speed. Along with the ability to use the chaos emeralds to...