The best places to get a baseball card appraised is your local sport card shop or if you have one available an auction house that deals in sports memorabilia. If none of those options are available, find a website that deals in this area and post a pic and ask.
There are Sports Card pricing guides published monthly which lists the values of sports cards. You can locate these in any book store or even supermarket magazine rack.
There are tons of places to get baseball cards appraised. The first place a person can go is to a local baseball card shop. The appraisal would probably be free or done for a small fee. The second place to get baseball cards appraised is through a company found on the internet.