During the years I've build up a list of memberships for my professional career. Below these are listed:
- Kivi-Niria - The Dutch Professional Engineering Association
- NLUUG - The Dutch Unix User Group
- ACM - The Association of Computing Machinery
In my humble opinion it is very useful to be a member of one or more professional associations. Not only for being a member, but more for getting in touch with people who are working in the same field and share the knowledge between them. Follow the links for more information.