Purchasing Consulting and Training Services
Legal:

Cornell University
The complete Uniform Commercial Code

Federal Acquisition Regulations (FAR)
You can review this site for the complete Federal Acquisition Regulations. More stuff than you ever wanted but some good procedures and definitions are contained in FAR that could save you time if you are developing a manual. If your firm is selling to the government this information can be helpful in understanding their requirements.

Gigalaw
Legal Information for Internet Professionals"