The National Certifiying Boards mentioned on this site, have varying levels of membership that are accessible to those who want to be a part of the ergonomics or usability communities but don't intend to become certified.
Depending on what, if any, training you have, you might join as an:
In Canada
HFIG: Human Factors Interest Group
In Australia
In New Zealand
In United Kingdom
In United States
Varying levels of membership can include you in newsletters; provide discounts on academic resources; allow you to vote in the organization; grant entry to conferences and workshops, and network you with other like-minded people.