I like freeware so I tried this one: http://taksi.sourceforge.net/
It is easy to use, the downside, support ended already (simply discontinued).
You will have to play around with it a little bit.
It has minimal/moderate impact on your performance (depends on all the settings, from resolution to codec use).
Do not forget that you need to install and configure codecs (xvid etc.).
If you want even easier applications use FRAPS and the like.
For FRAPS you have a free trial period.
But I do not remember if it has a watermark, if you use the trial version.