Jing--a free tool offered by Techsmith, the same company that sells SnagIt and Camtasia Studio. This allows you to record screencasts up to 5 minutes in length. You can save your screencast to your computer, or publish the video for free at screencast.com. If you take that route, you will have a URL you can post to your Web site or to any document (to save space on your hard drive). You do have to download Jing onto your computer, but it does not take up much space.
Socrative--a free interactive tool to engage students in a whole-class or small-group setting. Teacher must provide sample questions either orally or on a separate screen/document, but students can offer short answer or multiple-choice responses, which appear in real-time on your screen. Data can be presented in the form of a chart, or can be exported to an Excel document. This would be a great tool to use for test review, or as an exit slip. It can be downloaded onto mobile devices as well.
Wallwisher--an interactive space that allows students to collaborate in real time. Great for group projects. Photos, video, links can be embedded. Teacher can moderate content.
Xtranormal--a text-to-speech program in which you can create cartoon movies with your own customized script. This is not free, but there are affordable options for teachers to purchase monthly subscriptions (with options to add student accounts) or "pay as you go." To watch one of my Xtranormal projects, visit http://www.youtube.com/watch?v=YGNtXZTgASg.