Screencasting/Screen sharing:

Broadcast Yourself! 

Ustream, your own video channel  -- broadcast your lessons live, record for later viewing. uStream also provides a chat "channel" for your viewers to discuss while you are broadcasting.

http://www.ustream.tv/

Check out the "Educator Channel" wiki at http://edtv.wikispaces.com/ 

Check out the NECC Live channel wiki at http://edstreamtv.wikispaces.com

Mogulus... think "uStream on steroids"

(see review at http://blog.discoveryeducation.com/digital_passports/2008/06/13/mogulus-your-own-custom-tv-studio/)

http://www.mogulus.com/

Live audio-video communication, chat, content sharing, and session recording capabilities.

http://www.wiziq.com/

Upload, enhance and share videos:

Viddler

http://www.viddler.com/

Vimeo:

http://www.vimeo.com

Directory of tools:

http://www.c4lpt.co.uk/Directory/Tools/conferencing.html

Jingproject.com

Download for Mac or Windows. Instantly captures and shares images and video…from your computer to anywhere.

Screencast-O-Matic:

http://www.screencast-o-matic.com/

Web-based screen capture, uses your browser.

Wink -- downloadable program for Windows

http://www.debugmode.com/wink/

Kwout.com

Quote a part of a web page as an image with an image map.

Plugin error: That plugin is not available.

Berio = screen capture software for MacOS Leopard. 

http://www.juniortan.com/Public/Berio.html

Free, unsupported screen recording goodness that’s great for creating tutorial movies, demonstration content and illustrative animations.

Yugma: http://yugma.com/

Web-conferencing or one-to-one screen sharing. For Mac, Windows and Linux

Mikogo: a "Skype Extra" (PC only): https://extras.skype.com/1672/view

As a free online meeting tool, Mikogo allows you to share your desktop in true color quality with up to 10 participants simultaneously.

Simply click on your chosen Skype contact and invite them to a Mikogo free online meeting. Instantly you’ll be able to transmit your desktop screen to your invited contact’s PC.

Skitch -- For Mac users. Free tool (in beta now) for capturing and annotating screen images. If you haven't tried Skitch, run and get yours today!

http://skitch.com

Connect to other computers

http://Logmein.com 

will connect two pc users if both machines are turned on