If you can get a copy of software requirements it comes with good examples. If i have the luxury i create visual mockups of everything as that is easiest for clients to understand (I use balsamiq mockups). Once done with the requirements I get the client to go through them to either sign off on them or to send through changes. http://shop.oreilly.com/product/mobile/0790145385512.do
I wish they'd have some sales on physical books. Maybe it's just my traditional thinking, but I have a hard time paying $20+ for a pdf. I understand the publisher needs money, the author has to eat, and the printing costs aren't really a whole ton that you can reduce the price with, but it still just doesn't sit right with me.
I feel like and old curmudgeon.
Side edit: In what kind of strange world does the 2nd edition of an eBook still fetch $32 while the 3rd edition is $36?