Scott 2005 Specialized Catalogue of United States Stamps & Covers (2004, Paperback)

You will not find a better catalogue for US stamps. The "Scott Specialized" is the single most essential reference for collectors who wish to become/stay knowledgeable about US stamps. The numbering system used by Scott to identify stamps is the standard among stamp collectors in the United States. Most eBay listings for US stamps will refer to their Scott number.
Be sure to purchase the specialized edition if you want comprehensive details on stamp varieties, errors, booklets and panes, postal stationary, postal history, etc. It includes more information than Volume One of the Scott Catalogue which also contains listings for US stamps. The move to color photographs in 2005 greatly enhanced the usability of the specialized catalogue as a stamp identification tool.
Stamp values shown in the catalogue are updated each year to reflect market trends. Nevertheless, these values are only indications of value. Most stamps sell for a percentage of their catalogue value. You will find many damaged, heavily cancelled, or poorly centered stamps selling on eBay for 5% to 20% of their Scott Catalogue value. Desirable stamps in “GEM” condition are generally sold through other venues where they often sell at a premium over catalogue value.
New editions of the Scott Specialized Catalogue are published in the fall of each year, so the current edition will not contain all of the stamps released by the Postal Service during the calendar year. Since I do not focus heavily on current issues, I typically skip a year between my purchases of the catalogue. New collectors should not pass up the chance to acquire a catalogue that is several years old if it is in good condition and can be purchased at a fair price.
Once you acquire one – READ IT – I’m surprised by the number of people who never have a peak at “that stuff in the front” and never bother to look beyond the airmail section. The sections in the front and in the back of the book are essential if you wish to become a knowledgeable US stamp collector.

If you've started collecting and you want to know more about stamps and their cost, this is a great little investment. If you go to a reputable dealer, assessing your collection will cost you a fee. This book will help you identify specific stamps and break your whole collection down giving you an idea about the actual cost of a stamp you own or are collecting. You will still need to see someone professionally at some point, especially if you are thinking of selling, but at least you won't be in the dark about what you should be asking. Good luck and happy collecting...

This has been a wonderful resource. Much more complete and informative compared to dealer catalogs.

The standard of the hobby for almost a 100 years, history of sale price for major issues, complete identification guide included. Now with true color photos. Buying a catalog two or three years old saves alot of money, with little difference in stamp pricing.