Here's a handy link for all designers and for designer’s clients http://www.aiga.org/content.cfm/design-business-and-ethics Run by AIGA – American Institute of Graphic Arts, you'll find various pdfs to download covering topics such as: Client’s guide to design, Use of fonts, Use of illustrations, Use of software, Sales tax, Guide to copyright, Use of photography. It's a pretty comprehensive list, there's very little that isn't covered here.

Another book that overlaps on a good few of the above is: http://www.amazon.co.uk/Graphic-Designer-Without-Losing-Your/dp/1856694100 and another: http://www.amazon.co.uk/Its-Not-How-Good-Want/dp/0714843377/ref=pd_sim_b_2

Pic above is taken from this hilarious blog: http://thereifixedit.com