You can't be a programmer and not be aware of Stack Overflow, the programming question and answer site. It's unique blend of Q&A with comments and voting regularly shows up at the top of my searches and makes my programming days easier.
The underlying software, Stack Exchange, has been adapted for other discussions, mostly related to computing, and even some physics versions. These existing sites suffer from a lack of community probably because they didn't have a large enough community backing them up. Now, rather than a single person creating a new site for topic x, the people behind Stack Exchange have set up a place where a community defines the topic, commits to it and then a site is launched into a beta phase.
We (I don't know, part of the online physics community) are trying to restart a Physics Q&A site through this process. The type of site has been defined and we need to get more people to "commit" to participate there! Follow this link to the proposal, check out the sample questions and, if you can, commit to the project and help us make a definitive physics question and answer site on the web!