join.me - an incredibly simple way to share your computer screen with others. It works on both Windows and Mac allowing you to share your screen (and whatever is on it instantly). The simplicity of this site is brilliant.
LogMeIn - Remote access and desktop control software for all your computers.
Thinkature - brings the richness of in-person, visual communication to the web by placing instant messaging inside a visual workspace. Use it as a collaboration environment, a meeting room, a personal web-based whiteboard, or something entirely new.
Scriblink - is a free digital whiteboard that users can share online in real-time. Sorta like pen and paper, minus the dead trees, plastic, and the inconvenience of being at the same place at the same time.
Dabbleboard - an online collaboration application that’s centered around the whiteboard. With a new type of drawing interface that's actually easy and fun to use, Dabbleboard gets out of your way and just lets you draw. Finally the whiteboard enters the digital age!
Sketchcast - Sketchcasting allows you to record a sketch with or without voice. Explain something, have fun, or create art.
Nine Mind Mapping Tools (Concept Mapping)
Titan Pad - lets people work on a document simultaneously. In true real time.
TypeWith.me - Live text document collaboration
Sync.in - Live text document collaboration
Entri - Get feedback on rough drafts. Jot down ideas and share through Twitter. Free & simple with no signup required.
More Google Products - more Google web applications then you can shake a stick at...
Zoho - Productivity & Collaboration Apps
CrocDoc - Mark Up and review documents online, and collaboratively highlight and comment on PDFs, Word documents, images, and more!
Drop.io - Simple real-time sharing and collaboration
Wiggio - a free, online toolkit that makes it easy to work in groups.