This list focuses on stamp collecting and postal history sites. If you search Facebook and other social media sites, you will find even more connections to stamp collecting and postal history.
A high level message board devoted to sharing philatelic knowledge,
The Stamp Forum
This forum is a great place to seek answers about stamps, especially first day covers
Stamp Community Family
Large and vibrant forum covering a wide variety of U.S. and international stamp topics
Stamp Collecting Spot
Set up like social media to connect interested followers