White Boards

Online whiteboards offer a great way to collaborate.

Twiddla

Twiddla is one example. Participants can upload images, diagrams, web sites, documents or slides, as well as create things on the fly. There’s an option for voice conferencing as well as chat. No account is required to participate, but if you create a free Twiddla account you have more flexibility.

Cacoo

Cacoo is available as a plugin to a Google+ Hangout. Checkout the video conference page.