At the moment I am reading
buzzmarketing by Mark Hughes (not the ex-Man U player).
It is very good, but I am not learning anything
too much that I didn't learn from
Grapevine or
purple cow.
But the thing is that these books are as much about a perception shift than really teaching you to go and do x, y and z so immersing yourself in the subject is always good.
To be fair, they are all an excellent and entertaining read regardelss of how much crossover there is.
If I had to pick one I would probably pick buzzmarketing.
Sorry, I went on a bit there!
Ross