I'd recommend FRAPS, personally. It's cheaper and easier to use than Camtasia, IMO. While FRAPS is billed as mainly for benchmarking and recording game footage, it works just fine for general purpose stuff.
Camtasia has a lot of video editing add-ons with it, but it's expensive. $299 for the registered version. FRAPS is only $37.
You'll want a regged version of whatever you choose most likely, as the demo versions either limit your video length or add God awful looking watermarks.
A lot of people recommend Bandicam or Ezvid as well, but I've had good luck with FRAPS myself.
Worse comes to worse, just search Google for "best free fraps alternatives", no lack of results on that.
