Glogster is a platform in which you can create an inteactive poster that can include text, links, videos, pictures, etc. Project ideas might include a book critique, biography report, class webpage, history report, test/quiz study guide, etc.
Voki is a free service that allows you to create personalized speaking avatars and use them on your blog, profile, and in email messages. Uses for the classroom could include: add a voki to your class blog or webpage, give the homework using a voki avatar, students can share their favorite excerpt from a novel, and audio newsletter to parents, etc.
Wikispaces is a platform for simple webpages in which friends, colleagues, or families can edit together. Classroom use includes: have students edit a paragraph, students can write a story one sentence/paragraph at a time, creat a virtual word wall, complete a author study and post findings, create a wiki to share resources with students/parent/colleagues, etc.
Blogger is a free publishing tool from Google to share your thoughts, pictures, and video with the world. It can be effective in the classroom if used for: posting of homework, links to curriculum related activities, a weekly newsletter, book reviews, video clips, student resources, etc.
Twitter help keep up to date with what is going on in the world (especially education!). Despite what most educators think, Twitter can be useful in the classroom. See: http://goo.gl/azBT