Meetup is a popular website for finding groups of people that want to... well meet up. This link can be an important resource for finding events to attend through which you can network, and can be a useful tool for advertising one's own organizations.

A listing of blogs on Jewish topics, a great resource for finding interesting or informative articles on a variety of topics.

I spend a few hours a week studying with hevrutas over skype, and this website has been essential to my learning. Hebrew books can be expensive, and hard to find, but this website gives access to almost anything, including the entire Talmud, that you can think of. It's essential to my studies with others, and my own personal studies.