To become a successful stamp collector, you must be able to identify rare stamps and have an indication of their value. The best way to become familiar with rare stamps is to study images of them. There are several databases online that provide images of rare stamps. These online sources also provide some indication of value. There are several online resources that actually sell stamps, and there is one that just serves as a research index.
View rare stamps and learn their value on Find Your Stamp's Value. This website has a complete database of the rarest stamps, but does not sell stamps. You can search for a stamp's value using their search tool. Just enter the scene or picture portrayed on the stamp (for example, flag) with its denomination, and the search tool will search the database for similar results. All results that match the query will be listed with a picture of the stamp and issue date. To learn the value of the stamp, you must be a member. Membership as of April 2014 costs £11.95 for 31 days.
Browse rare stamps and learn their value using the Cherrystone Auctions website. Cherrystone Auctions specialises in auctioning off stamp collections. It has a database of all of its past stamp auctions, which is comprised of the world's rarest stamps. Each past auction lot has a picture, description and issue date for the stamp, along with an estimated value and the actual sales price. This site will give you a good idea of what rare stamps actually sell for, which can often by less than their estimated value. There is no fee to browse this directory.
Look at rare stamps and find out their value by using the database on Mystic Rare Stamps. This site actually sells rare stamps from the United States and from other parts of the world. This website displays photos of all rare stamps listed, and some stamps will also list a catalogue value along with the website's sales price. There is no fee to browse this database.
Search for stamp photos and values using the Delcampe index. Delcampe is an online marketplace for stamp collectors and sellers. Each stamped featured on the site has a photo along with its retail price. Delcampe has thousands of rare stamps from all over the world and will display the retail value of a rare stamp. There is no fee to browse this index.