Swimming! I went 3/4 times a week, swam 40/50 lengths and ended up loosing 2 stone in 3 months. It toned me up too, you use a lot of muscles to swim
This sounds promising, I'm about to sign up for the gym and I plan to go swimming every day for next month before I go back to uni. I don't need to lose any weight (but I won't complain if I do )but I do want to tone up.