Mass Effect is instore in HMV as a special Sale item (purple sticker) for £10.
Cheapest online is currently £17.99
Now here's the rub. HMV also sells the Classics edition at £19.99 where there is a bonus cd which has bonus download content. For info on this go to Play.com's site:http://www.play.com/Games/Xbox360/4-/9351470/Mass-Effect/Product.html
However, getting the game for a tenner is great - not too concerned about the bonus content for that price.
Not sure if I lose out on the 'Bring Down The Sky' downloadable content - but hopefully its a free download anyway!