Found "Official Price Guide to Classic Video Games: Console, Arcade, and Handheld Games" whilst hunting through Amazon for gaming-related books to add to my shelf.
http://www.amazon.co.uk/exec/obidos/...037112-9956403
It doesn't say why it's "offical". Now of course it's not a patch on the DP guides but it's also going to be a hell of a lot cheaper for me to get in the UK - has anyone here read a copy? The reviews on Amazon US seem pretty good but there's no saying the reviewers know their stuff.