For those of you who missed this deal a few weeks ago it is now back! Blizzard are offering the base pack which includes all expansion packs, except for WoD, and 30 days free full subscription.. Which will give you access to all features of the game!
Amazing offer seen as subscription is still around £10 per month, get for half price + all expansion packs.
Please be aware this offer will only be useful for new users/accounts which do not already have the base pack.