I just downloaded and printed (all 250+ pages!) the e-Consultancy PPC Best Practice Guide, which I must say is a fantastic piece of work!  If you’re not an e-Consultancy member, you should be, even if just to get this guide – but over and above that, they’re a great resource for affiliate marketing & online marketing information.  It’s got great information on how to run a Pay Per Click campaign and even for beginners or pro’s it’s a good roundup of best practice.  It’s probably the most up to date guide out there that I’ve seen in a very long time.  I highly recommend it for everyone in the PPC space – I’m still shocked at how detailed it is!  They charge $179 for this report or $269 for full access to all their reports – we subscribe to the latter.
Disclaimer:  There is no financial relationship between myself/incuBeta (other than the fact that we’re a paying subscriber) and e-Consultancy and they did not ask for this plug!