With my next baby, I'm definitely signing up for the Parent and Pram exercise class at Regent's Park, The Hub. Getting fit was always a goal with child #1 that never fully materialised (imagine that!). A class that actually incorporates the child/pram in the exercise routine sounds positively brillant. No more excuses for me. More info on their site.
The Hub also offers mother & baby yoga, running and walking groups, pilates, body conditioning, and more (all on a handy pay-as-you-go basis). Click here for a list of class descriptions.