Being involved with 4-10 professional American business associations can do wonders for acquiring new business and learning new skills.  One of the most prestigious business associations is the Entrepreneur Organization (EO), which used to be know as the YEO.  Their are chapters in most major cities across the United States ranging from 30-180 members.  Your company needs to make over $1 million and have at least five employees in order to qualify for a membership.  Here are a few reasons to join the EO and at least another 3 business organizations.

Networking
There is no substitute for face-to-face networking.  In the business world this can equate to millions of dollars in new sales.  Make a point to never talk about your business unless someone asks you.  Your goal should be to ask every person in the room about their business and how they got started.  Naturally, they after speaking about their business they will reciprocate and ask you the same question.  They will feel inclined to actively listen since you were so intrigued with their business history.

Learning
The best business associations invest 50% of the dues in monthly speakers who are experts in everything from marketing to raising capital.  By attending all of the events each year, you will build an arsenal of knowledge that will help your business grow.

Problem Solving
The EO and many close knit associations have sub-groups where non-competing members can come together to share their problems and help eachother come up with solutions.  Being involved in an association, allows you to leverage the entire knowledge base of the association.  This keeps you from having to be all alone when you have a business problem.