Just seen these on my recommended list (despite already owning them) on Amazon.
Most people might already have them but might be useful for someone.
Wrath of the Lich King - £1.64 / £3.63
Cataclysm - £2.49 / £4.48
Mists of Pandaria - £2.47 / £4.46
(Deal link goes to Wrath, links to others in first comment)