Older, antique dolls are much more valuable than newer dolls. Once you've learned the type of doll you have, the material it's made of, and its age, you can get some idea of value. In order to identify your doll (which I am thinking that you have not or else you would have mentioned it) then you can search out values. There are many books on the subject including:
"Jan Foulke's Guide to Dolls: A Definitive Identification and Price Guide" by Jan Foulke
"200 Years of Dolls: Identification and Price Guide" by Dawn Herlocher
"The Collector's Encyclopedia of Dolls" by Dorothy S. Coleman
There are many more such books to help you learn more about older dolls. Price guides can not be depended on to reflect current values.
You might want to check out the United Federation of Doll Clubs.
To learn the value of your doll, once you have identified it, there are several sites that you may try including:
You can also check sold prices on eBay by clicking Advanced Search for completed auctions and sold doll listings.