One of the blogs I love to read each day is this one http://justcats-deb.blogspot.co.uk/ and it was Deb who recommended the cat play toy 'Cats Meow'. After reading about it I purchased one online and you can see for yourself that it was a hit with all 5 of them.
Our lot have a cat flap and it is open all day long but after the initial nose outside in the early morning they don't bother going out much. This keeps them amused for ages, they take turns at giving it a bat and when one leaves another goes in and has a go. Well worth the money.