There are many forums on the net to talk about cards.

NET54 Vintage Non-Sports Cards

This site is an online, moderated forum for discussing Vintage Non-Sports Cards and other Non-Sports Memorabilia like pinbacks, silks and leathers.

Non-Sport Update Card Talk

Welcome to Non-Sport Update's Card Talk. Card Talk is a free service of Non-Sport Update magazine, the leading publication covering the non-sport trading card industry.

Vintage Hockey Forum

This site is about hockey collectibles not only cards although they are a big part of the discussions.

Collectors Universe

Mostly modern cards discussion board.

Net54 Baseball.com

Not part of the NET54 family anymore but THE board to discuss baseball cards (and some other sports too).

Non-Sport Card Forum

Non-Sport but also CCG-TCG.

ConnexionHCK.com

Forum d'échange de cartes de hockey en Français. French forum for exchanging hockey cards.

Cigarette Cards

Cigarette cards collecting forum.

Rubber Uglies, Topps UGLY Stickers, Slurfies, Finger Monsters & Jigglers FORUM

There is a section dedicated to monster cards.

Basket-Ball Trading Cards Forum

Forum de discussion de carte de basket-ball en Français. French forum about basket-ball cards

Full Count Forum

Vintage Baseball Cards Forum

Freedom Card Board

Sports and Non-Sports

Cryptozoic Forum

Modern Card manufacturer