I have just finished reading 'Writing Effective Use Cases' by Alistair Cockburn. It is a truly great book and I would strongly recommend anyone about to embark on a requirements project to read it.
I have read a number of UML books in the past and nearly all of them have passed off Use Case writing with a sentence like 'A complete discussion of this is a topic for a whole other book'. Well this is the other book.
In just 230 pages (there is little waffle here), Cockburn manages to give the topic very thorough coverage. The number of different Use Case styles presented and the discussion about when to use each particularly impressed me. The examples too are surprisingly complete with almost no ... in.
My only criticism is the books structuring with some chapters being 20 pages and others less than a single side. This is only a small point though, and will only cause you a problem if, like me, you like to read a chapter a day.
All in all, I wish I had read this years ago.