The people over at www.bombergames.net have been working on a Streets of Rage remake for over 8 years. Started on March 17, 2003, the game is finally out.
The remake features a whopping 103 stages, all the characters from Streets of Rage 1-3 have received new moves with remastered sprites. Some new characters have also been added. Enemy sprites also received the remaster make over as well as RGP color corrections for the SoR 2 and 3 goons.
A lot of extra content have also been included such as cheats, editors, customizable options and a volleyball mode. SEGA is aware of the project's existence and hopefully they won't make a fuss about it. After all it did take them 8 years to complete.
The game is available for free on their site and if you're feeling generous, donate to them via Paypal for all their hard work.