What are some common laws?

Good Wiki article on the Common Law. Easy to read.

http://en.wikipedia.org/wiki/Common_law

(Sorry about the reading.)

a common law in ohio once was if a dude and chick lived together and held themselves out as being together after so many years of doing so they were considered a 'married couple' under the state's common law marriage and entitled to whatever benefits come from being imprisoned to another person.

Look at the traffic code. It is the most uniform of laws throught the United States. In al 50 states, pedestrians have "the right of way" by law and all motor vehicles must yield to them.

Define what you mean by "common"