im not up much on stone or whats good for a beginner, being a beginner myself, but i have been knapping the heck out of obsidian. there is a rock shop in town that has it $0.60-$2.00 per lb for rocks depending on type of obsidian. im sure someone will chime in with something better for begginers (and ill go out and get some of that) but for me its working fine.
As for youtube i use mozilla firefox and an addon called downloadhelper, along with flv player you can download the entire streaming file to a media file with .flv extension and have it all there before you play it. (also helps catalog vids you might want to watch again later) and if you would like to take it 1 step further there is a free open source video converter called "super" that will take the .flv file and make it into any kind of file you want (including burnable to DVD-mpegs) hope this helps
Best of luck
Dustin D