Game currently have the Prima strategy guide for Mass Effect for £4.99, down from £12.99. That's not a bad deal, but they also have the Collector's Edition of the guide (normally £17.99) for exactly the same price - £4.99 delivered.
You get the 288 page strategy guide, a large poster AND a hardback 175 page book showing the artwork of Mass Effect.
I ordered mine yesterday, it arrived today and I'm hugely impressed for under a fiver :)
Possible Quidco / game reward points as well.