Noesis in a company who makes video tutorials like those on youtube just, the guy who make them made HL2...

The videos are quite expensive, but it might be worth it; I learned all I know from "Advance source level design".

You could also torrent it...


References:
http://www.noesis.com
http://www.youtube.com/noesisinteractive

Edit: Fixed spelling.

Yeah I was looking into that a while ago, but as you guessed I was too cheap to purchase it for the $50 so I don't know how good they are.

I found the video usefull(as mentioned above..), but still expensive, they did alot of other stuff; Machinima and coding Etc.