If I was in this spot and wanted to think about a lawsuit, I would immediately think, "How can I find out their side?" I don't know law or what is within reason but I know I would find out who saw what and some stories. Whether it be friends posing as patrons and pointing out the bouncer mentioning how they saw him toss "Some dude" the other night. He may brag or what not. Also, I would find out if police have records of eye witness accounts, if not, why?? Ambulance, drunk guy out cold, seems like cops would be all over. Cameras? I would canvass the shit out of the area. An ATM may be your best friend (unlike most of college).
I would dig myself without doing too much to see what I really have ahead of me. While some may not be used in your case, you at least know if you should pursue or if you were a total jackhat that night.
What you find could be enough for a lawyer to take the case.