Advice on video software

I apologize if this has been asked here or somewhere else. I would like to capture some video off the internet (Youtube for example). nothing big, just some video (NOT for commercial use or to make illegal copies, just for my own personal use).
Is there any video software that would allow me to do this?

Thank you for your responses.

I recently downloaded the latest realplayer app and that came with a really cool downloader which is simple to use. Once you download the files they will be in Flash Video format (flv) but you could you a program like MPEG StreamClip to covert them into what ever you like.

RealPlayer Get the free one, it does all you will need. Hope this helps.

GetTube.
It lets you grab videos from youtube, wether youre using safari or firefox, and all in just one click, like seriously. all you have to do is click on the browser you are using and it will ask you which video of the ones you are watching you want to get. and itll start downloading to your downloads folder.
awesome.

When you are watching a video on YouTube, go to the 'Window' menu, and click on 'Activity.' Then look for the line of writing with the largest MB/GB size. Or alternatively, double click on every one until is starts downloading.
Download a free version of VLC player for Mac OS X, then play the flv. files with VLC player.

Regards.

I thank all of you for your clear answers. I will try them all.