CafePress
Custom designed (by you) products like t-shirts, mugs and other merchandise 

Colour Span
File Size and Output Resolution Calculators

C thru ruler
Graphic arts rulers

Graphic Brain
Specialized search engine, focused on the technology and products used in the graphic arts, printing and publishing industry

International paper sizes

PackExpo
Packaging links and information

Pixeltees
Online t-shirt making company similar to Cafe Press

Symbols
Online encyclopedia of graphic symbols! Symbols.com contains more than 2,500 Western signs, arranged into 54 groups according to their graphic characteristics. In 1,600 articles their histories, uses, and meanings are thoroughly discussed

Thomas Register
Online resource for finding companies and products manufactured in North America

US Postal service Mailpiece Design