sounds like a commercial, doesn't it...
I found the Theatre Monkey website useful when buying concert/theatre tickets in london. It has tips on how to get good tickets, and has a detailed seating plan for all featured venues, each one colour coded according to his own system. Each section in each venue is described in detail, and you are told which seats are "incredibly good value" and "a total rip-off".
It's main focus is West End theatres but also features concert venues, e.g. Wembley Pav, Earls Court, Hammersmith, Albert Hall.