Power walking - try taking your cat out for a walk on a harness (yes, a harness!). Cat harnesses are available from your pet shop. While you're out, encourage your cat to jump and play using natural 'toys' like piles of leaves.
Toys - homemade or pet shop toys help to encourage your cat to get moving.
'Catch the Light' - shine a white light torch on the walls and let your cat play (do not use a red light laser as it can damage your cat's eyes).
For a few more tips on exercise and weight management for your cat click here.