Function Modules

Hi!

I was wondering where can I found any function module manual. Is it supported in SAP? I just want to have a list of them so I could use them while programming in ABAP (not for particular functions but general overview).

I found at Amazon.com a book "Common SAP R/3 Functions Manual" but I'm not preety sure if it isn't a waste of my money. Maybe somewhere in the net I can find these?

Any ideas?