Most of the links on the main page take you to resources that can be used immediately. They do not require a person to purchase something and wait for delivery of a product, or to send off a question and wait for a response.
However, sometimes a situation may arise in which the expertise of others is required. For these situations, below are listed several forums and Usenet groups in which people may interact. I have found both the forums and the Usenet groups to be very good, with many competent professionals interacting on them. In addition to the exchange of information, the forums provide an environment in which a community develops. And each forum has its own unique "flavour", as you will note if you spend time in them.
The Usenet groups, do not provide the same "community" environment, but are still excellent sources of information.
Rocket and Space Technology
Cygo Space Initiative
Nice site by George Perkins, who also is the owner of the Yahoo! Aerospace Engineering Group.