Like many people my age and older, I am hearing impaired. Specifically, I have lost hearing in the upper ranges. I find that I can manage reasonably well in face to face conversation, but I have a lot of trouble with recorded video. I use VLC which has a built in equalizer, and Songbird which has the same. However, I cannot use VLC for online videos unless I download them first. I also can't use VLC for Skype.
Fortunately I found a free and open source equalizer which can be set to affect all audio on my laptop. You have to configure it via a text file but that is not difficult. I am also in the process of building a simple GUI with sliders which will modify the config file. If anyone is insterested you can find 32 and 64 bit versions of Equalizer APO here.