What is a good search site for background checks?

If you are asking for free and reliable there is no such thing. Some sites are better than others.

If you are looking for a person's background/criminal record many States have info available on line.

I have never found one site that is reliable, other than the Government sites. Obviously you would have to switch from one site to another (State, County, City) and compare the info IF the info is available on line.

Why are you doing a background check?