This morning, on my way to work, I happened upon a collision scene. A schoolbus with a very mangled bicycle underneath it, and a scraped and bloody rider. The driver had, apparently, failed to check his mirrors before turning, and the rider got hooked. Fortunately she fell off before the bike got sucked under the bus's wheels. She was scraped up but wasn't majorly injured. I called 911 anyway, to get the police to come so that she could file an accident report. Well, because of either standard protocol or not hearing "no major injuries," they dispatched an FDNY fire truck and ambulance, out of which tumbled six or eight people who proceeded to immobilize her spine.
Her bike is locked up on the SW corner of Bedford and S.10th street in Brooklyn, and if you see it, take it as a reminder to stay safe and smart out on the streets.
If you get hit, even if it's minor, call the police and file a police report. It serves as an official documentation of the collision (I avoid using the word "accident"), which you absolutely need if you want to follow up with the driver's insurance company. That is, if you want them to pay your medical bills or replace your bike. You never know what will hurt after the adrenaline wears off, and you never know what's broken that you won't see on the first pass over the bike. Maybe your frame is cracked. Maybe you've got a minor concussion. In New York, the car driver's insurance company has the responsibility for covering those things. File a police report and then submit a No Fault Claim with the insurance company.
There's lots more information floating around. I'd start by checking out the Know Your Rights manual, which is aimed at messengers. Also, Transportation Alternatives provides a list of cyclist-friendly lawyers, should you need one.
If you're going to be on the street a lot, you entertain the possibility that you'll get hit by a car. Know what to do so that you're not left in the cold, with a broken body and a broken bike. Knowledge is power.