Youtube (http://www.youtube.com) is an excellent source of video material. I guess most of us already know that.
Most people also probably know that you can download videos from there if you use Keepvid (http://keepvid.com/). I don't trust things to stay where they are on the internet, so if I see something I like, I grab it. Hence Keepvid works really well for me.
Recently I found that I'd downloaded quite a lot of things that I wanted to compile into a single DVD. That way I could watch them on the TV. I looked around for something to convert the Flash Video format (FLV) used by Youtube and I found RivaVX (http://www.rivavx.com/).
Now, I can't vouch for the commercial product, since the freeware product did all that I needed, but I think it's worth mentioning that video conversion software that comes without bundling and without awful watermarks is rare. So RivaVX are to be congratulated - check them out if you want to do something similar.
So, to summarize: I used Youtube to find the videos, keepvid to download them, RivaVX to convert them to MPEG and Nero to make the DVD. Nope, it's not exactly straightforward, but surprisingly, it worked.
Oh - and there's some excellent instructions for the Riva conversion at this site: http://forum.videohelp.com/viewtopic.php?t=259578