There are a lot of products available which provide some level of synchronous audio, video, or collaboration and it can be a lot of work going through the process of assessing each one, for features and for integration with Moodle.
The Moodle community website has a forum dedicated to discussions about the various web conferencing plugins, so this is a good place to look for information about what is available and useful.
The community forum is at http://moodle.org/mod/forum/view.php?id=7797.
The Moodle community website also has a plugin database of add-ons which is open to download by everyone. If you search through this with a variety of keywords such as conference, meeting, and so on, you will find a range of applications. Some of these are up-to-date and some others have not been updated in over a year. Some of the better known ones are:
The plugin database is found on the Moodle community website...