Mine get bored really quick too and I have a whole pile of catnip toys and others that they are totally disinterested in.
One of the best things mine like is the da bird but I change the attachments all the time. I volunteer at a horse rescue centre / farm and every weekend I go round collecting things to put on the end of the da bird. People think I'm a bit nuts but I get lots of things that smell, taste and look interesting. Then I just attach them to da bird. They have chased chicken feathers, peacock feathers, horse tail hair (from a trim), plants, crows feathers, seagull feathers, freshly sheared wool. They love it, and it's free so I can just throw it when they are bored or have killed it.
Mine also love a kids tent from Argos. It collapses, has 2 entrances and I have cut a few holes in for extra access. They play for hours in it and don't need me doing a lot.