CamFrog
Windows | Mac OS | Linux (Server only) | iOS | Android | Windows Phone
CamFrog lets you set up Web-based video chatrooms where you or others with a webcam can join a conversation. One-on-one conversations are also an option and you only need a webcam to be seen, not to see others. Plus it'll do voice and text if you don't want others to see you.
Cisco WebEx Meetings
Anyone who holds a lot of online meetings has probably run into Webex. It's a standard way to share a desktop and do an online whiteboard, but it also offers VoIP features, even on the free level that includes standard-quality video chat. Naturally you'll have to pay for high-definition video.
Jitsi
Windows | Mac OS | Linux
Like your free software of the more open-source and unlimited variety? Jitsi (formerly the SIP Communicator) fits the bill nicely, with almost nightly new builds of the multi-protocol software; it's ICQ for video and does SIP or XMPP-based video and audio, and works with Yahoo Messenger and AIM for text chat.
ooVoo
Windows | Mac OS | iOS | Android | Facebook
ooVoo takes on Skype directly by providing features like IMs, free voice calls to any phone, screen sharing, and file sharing—and on the video side it offers group video chat with up to 12 people, along with video call recording directly to YouTube. There's a Facebook app that lets you join a video chat right from the Web. It's ad-supported unless you make an upgrade to premium for $2.99 a month.