Here are a few useful Links:
Organizations--
American Philatelic Society
The APS is the largest, nonprofit society in the world for stamp collectors.
American Philatelic Research Library (APRL)
The American Philatelic Research Library is the largest public philatelic library in the United States. Its holdings include many of philately's classic periodicals, and it receives more than 400 current periodicals from around the world.
American Revenue Association
The ARA is the largest, oldest and fastest-growing national or international society devoted to revenues, tax stamps, stamped paper, telegraph and railroad stamps, and general non-postal Back-of-the-Book material.
Meter Stamp Society
The Meter Stamp Society is dedicated to the collection of postage meter stamps, topical slogans on postage meter stamps, computer postage (CVP), framas, photostamps and similar items.
Stamp-oriented Sites--
County & Municipal Revenue Stamps
Multi-state listing of local revenue issues
Florida State Revenue Stamps
Images of, and articles about Florida State and Local revenue stamps
State of New York Stock Transfer Stamps
High resolution color images of 286 varieties of these stamps. Content is nicely indexed, with examples of key identification features, and usage examples.
Eric Jackson
World's leading philatelic firm dealing in United States and Canada revenue stamps and related literature.
DK Enterprises
Large selection of Revenues, Postal History,Military/P.O.W./Censored, and US & WW Stamps. ALWAYS Buying!!
Blogs--
Revenue Stamps
This group is devoted to exchanging information on the collecting of U. S. federal and state revenues. The blog is moderated by Ronald Lesher.