As far as free ones go, that cam studio lux pointed out is the most widely used, with lots of features.  You can save to many different audio and video formats, like Mp4, AVI, with many customizable options.  I used Webinaria before for a video presentation, and while it was very easy to use, I wasn't quite happy with the control I had over the output.  It can save out to AVI or convert to compressed FLV, but there aren't many options for tweaking the capture results or the output quality of the video. I think they give you some preset options.  Camstudio has tons of customizations to tweak the output video, including frame rates, and HD, but it's slightly higher learning curve.  I like the Webinaria editor for quickly adding titles and stuff to the output, but I do most of that work in Movie Maker.