I actually started Spinnin class since last November (I know don't laugh) and lost about 22lbs over winter and riding early this year already with my riding weight.
Spinnin keeps you fit and cardiovasculary in shape.
It helps to be motivated by a good instructor with great music and spinin in the back row of the classes with a sea of nice tight bums(female that is)

http://www.quadloft.com/hometheater- new HT