All the online tools listed below are free. Yes they are really for free!
(Here is another list of online tools you can use. It's not all free but there's some really good stuff there.)

Blogging Tools

Blogger
New Blogger
edublogs

Wiki Tools

pbwiki
This wiki site has a new user friendly tool bar to make page creation even easier.
wikispaces
wetpaint (more than a wiki, more than a blog, it's uh ... wetpaint?)
seedwiki

Audio Tools

audacity
evoca
vaestro (add it to your blog)
yackpack
imeeb an easy way to embed audio into your wiki or blog
www.WiZiQ.com

Video Tools

google video
YouTube
blip.tv
www.WiZiQ.com
Viddler.com
Animoto.com
voicethread.com
link is here

Screencasting Tools

camstudio
www.WiZiQ.com
www.authorGEN.com

Image Tools

flickr
Gliffy
Google SketchUp (Draw in 3D)
Photobucket
Here is an example of what you can do with photobucket.

Slideshow Tools

www.authorSTREAM.com Upload and share your PowerPoint with narrations , rehease timings ,animations for excellent flash output view .You can use the embed tags from here on your blogs.You can also bulk upload from Desktop using authorPOINT Lite - a free utility by authorSTREAM. You can also upload presentations with annotations and captured audio as captured using authorPOINT 3.9 - presentation capturing software .You can www.authorGEN.com for more details
spresent This is a flash driven application that gives you the interactivity you want if you are recreating a powerpoint presentation.,
Here is an example of what this application can do.
slideshare
This is an excellent site to upload powerpoint presentations to. If students want to publish powerpoint slides this is the place for them.
bubbleshare
Here is a great example of a student's post that uses bubbleshare
thumbstacks
Here is an example of a student's post using thumbstacks
empressr
slide.com
Here is an example of what students can do with slide.
zoho Many different applications at this site including presentation and word processor. You can upload ppt and word files as well.

Web Apps ThinkFree (WP, SS, PPT, PDF)
Google Docs (WP, SS)
irows (SS)

Even More Tools

123.jpg
Go2web20.net