Metal selection 101

Hi All,
Here in Phoenix we have a good surplus metal place called 'Davis
Metals. Lately I've been wandering around trying to pick out useful
steel to machine.

My goal is to find a steel that is easy to machine and can be sent
out to be hardened if needed. This will be for general purpose
toolholder/vises etc Any suggestions?

What field tests can be done to determine if a piece of scrap steel
may be useful for machining? Tim mentioned the spark/grinding test,
and I was also thinking of a spring loaded punch and battery powered
drill. Are there tips from the experience pool on this...

Thanks,
Lee

p.s. Has anyone else spent time entering a long post, then hit "post"
again by accident when you meant to hit send? what a pain! For now on
I'm composing offline first!!! aaarrrggggghhhh!!!