A site which loads with resources for both the designers, Offline (Print Media) and the Online (Internet) professionals.
Most of the time we get stuck with out knowing the right dimensions for instance when ever we wanted to make a CD label, we go ahead and start measuring a CD and then design them. This site has enough resource on all possible office related stuff. And it is all free to download.
Educate yourself with the right design terms. You could learn how many different types of folder exist and how to differentiate them.
So check out the site Designer toolbox