The first thing you should do is get the artists name. If you have that try a search on the internet, google. ask jeeves, etc. then the library. Those are the only free sources I can think of. Some times outfits that specialize in estate sales have experts. But if they offer to take it of your hands, don't go for it. It probably has some value. A last resort is an auction house. They do charge but they will give an honest appraisal.
good luck!
