Here you will find all the information you need about buying stamps and selling them. You can find numerous stamp catalogs but these are usually rough guides.
Where to Buy Stamps
Stamps.com vs. Postage Meters - Save at least 50% Buying Postage
FSNB Mail Stamps For Sale By the Book
Where to Buy Stamps: A Complete Guide to USPS Stamps
PTA Blackboard Sheet of Fifty 8 Cent Postage Stamps Scott 1463 on
How to Buy Postage Stamps Without Going to the Post Office
WATCH, Good Question
Comics~Be A Sport & Spend A Cent~Man W/ Cigar Buying Stamps~PM 1915~Vintage PC
19 Great Places To Buy Stamps
6 Ways to Buy Postage Stamps Without Going to the Post Office
YS1966C - 1966 Complete Commemorative Year Set, 17 stamps - Mystic