The AIGA (American Institute of Graphic Arts) has published
many legal and business ethics guides and books to assist
creative professionals and the people who hire them.

The AIGA has also participated in developing state sales tax
laws regarding design, tangible property and digital files,
making design professionals and their cilents’ lives much easier.

Below are pdf files of their published guides.
I hope everyone finds these helpful

AIGA Client's Guide to Design
AIGA Business & Ethical Expectations
Print Environmental Responsibility
AIGA Design Services Agreement
Sales Tax
Guide to Copyright
Use of Fonts
Use of Photography
Use of Illustration
Use of Software