What forums or websites have an active bitcoin section? Which websites have active bitcoin communities with discussion that is going on?
Bitcoin Talk is currently the most active.

The bitcoin reddit also has a fair amount of traffic and discussion.

After that, it falls off pretty significantly.

Talk Gold has some discussion, so does bitcoin.org.uk.

bitcoinforums.net and other forums are sparse. (See link to wiki in Chris Acheson's post for a list of all current forums)

There are of course often discussions about blog posts or news items on tech related blogs like Slashdot, Ars Technica, Wired, etc. The same is true of some sites dedicated to online gambling, and some Tor forums dedicated to the Silk Road and similar projects.

There have also been some longer threads that are especially useful for miners at the Overclockers Forum