Still a kitten, my cat loves to play and his favorite things are the cheapest toys! And overall, his favorite are cat springs!
Not these in particular (got a pack of ten for $1.99 locally) and the cat can keep himself amused for a long time with these (until he loses one under a piece of furniture that is). He likes anything that appears to move on it's own.
Even more fun is that he loves to play fetch with these! The cat is part dog, lol. He has me fling them across the room (like a rubber band) so he can chase them. And waits for me to do it again.