G+ hangouts, Skype group video calling for six, Fring for four.
Group video seems to be all the rage.
Options now include Paltalk, which offers 10 streams in a group video chat (the host needs to install the application). Spreecast will soon launch with four video streams and unlimited voyeurs.
There are plenty of established operators, though the results are a bit of a mixed bag.
Sifonr is a web app that allows you to create an instant video chat room without registration. The room can be public or private.
Tokbox offers up to 20 video streams but requires an account for each participant. It offers an API (application programming interface) so the tool can be integrated into your own website. The charity platform Causes has used Tokbox to enable fundraisers to record a video message to increase the impact of their appeals.
TinyChat is a busy site with multiple casual chat sessions underway. Observers need to register or sign in with Twitter or Facebook, but you can also participate in up to 12 chats at a time. The content is peer to peer and unmoderated, so may be unsuitable for minors.
Some services simply provide the same tools as others and represent an alternative, but little more. For example, VPhonet is a Polish competitor to Skype offering video conferencing via an application that requires a download.
Judging from recent activity, this sector is only going to get busier.