I use Slideshare quite often in order to take a PowerPoint presentation that I used at a face-to-face professional development session and place it for viewing on a website. It's quick and easy. I usually have a website for most of the professional development presentations I do with resources, etc. and so this just makes it very quick and easy to add the PP that I used also.

Voicethread is a versatile web 2.0 tool that I recommend to many teachers. It can incorporate images, text, and speech into one product and is a great alternative to traditional reports many times assigned to students.

EtherPad is a web-based word processor that is an alternative to GoogleDocs when you don't need the complexity of having accounts, permissions, etc. A free public etherpad is shared with others by sending out the URL. Any one can access, edit, etc. just from the URL. I have found this tool very useful in collaborative meetings/planning sessions as a way to quickly draft and edit work collaboratively.