Fraps. Its not the easiest to use but once you get use to it its pretty simple. Its records in HD. But it only records for a set amount of time. So you will end up with clips and have to use an editior. Which I prefer so I can edit out any mistakes or unwanted clips.
this is the best one I know of and it doesnt give me any problems, it called hypercamerav2 but they also got a v3 but I prefer v2. just go to google and type in hypercamera free download and it should be one of the first links. good luck on your videos
bandicam is free and let's you record up to 10 min at a time, but it does have a small watermark at the top of the screen. you could also use ezvid but i highly recommend bandicam or paid version of fraps especially for there simplicity