Non Apple components in Mac

Guys

I am seriously considering switching from PC's to Mac because I think the Mac's integrated video handling abilities are superior.
What I need to know however is:

Will PC components work with Mac boxes
e.g. CRT monotors, RAM blocks, hard drives, graphic cards?

Many thanks for your comments

Pierre

monitors.. most of them yes.
RAM blocks... hmm doubtful
hard drives, yes
graphic cards.. some. (most no)