The greeting cards business is a nearly $7 billion industry according to the Greeting Card Association (GCA). There are number of resources that track the greeting card business. There are also industry organizations and associations like the GCA. There are also awards and exhibits. Here is a list of some of the top resources:

Gift Shop Magazine

Greeting Card Association (GCA) - U.S. industry organization

Greeting Card Association (GCA) - U.K. industry organization

Card Maker Magazine - a magazine about making cards

GreetingCardWriting.com - a resource from Sandra Miller-Louden

Greetings Today - a British publication covering the greeting card business

LOUIE Awards - annual greeting card awards

National Stationary Show - The NSS is an annual for all things paper.

Party & Paper Retailer Magazine - industry magazine

Progressive Greetings - greeting cards magazine and official journal of the UK Greeting Card Association

Writing for the Greeting Card Industry - article from The IWJ