Magic Self-Stirring Mug - £3.99 delivered from Play.com
Quick Google search shows this as ~£11 in most shops.
Description : Go stir crazy with the Magic Self Stirring Mug! No more sludgy sediment at the bottom of your mug of hot chocolate, soup, coffee or cocoa. Stir in sugar at the press of a button. The mug has a compact paddle wheel spinner in the base. 2 x AAA batteries included.