My Mum introduced me to one of these weighted fitness hula hoops! I used hers over the summer and I'm hooked. It's a great way to burn calories and tone up your tum. It's also great for strengthening inner core muscles and helping with posture and back pain. I have a bad back and it does seem to really help! Plus it's much easier than it looks, in fact it's fun! Turn the tunes up loud and hoola!
nb. you may feel slightly bruised after using it to begin with (I did!), it's recommended you use it for short periods and then build up the time.
You can buy them on Amazon for around a tenner. Enjoy!