One toy that none of my kitties seem to tire of is this track ball with the center to scratch on - it is cardboard that is replaceable. I got it at Wal-Mart for less than $10 too!
Robbie found it right away...

Here is Eliot with it too - from last year sometime...

I know Emily and Eliot played with it even as kittens as well but can't find any pictures just now