I have already mentioned in a thread already today, and am not getting commissio for it, but I started Body Pump classes at my local leisure centre recently and really noticed the difference.
In a class of 14, five are men, and the age range would guess is from early 20's - late 40's but is open to anyone.
It's a class that uses weights in a variety of exercises to tone the different muscle groups in the body and in five weeks loads of people have mentioned to me about my body shape, I have toned up so much and have muscles that I never had before! it's good fun and they play great music (you do the programme to a set of songs that are changed every 3 months).
Swimming is also good for toning, as is spinning, yoga / pilates, martial arts and dance.
I am only speaking from personal experience, and I think it is always good to try loads of things to find out what suits you.