Pet stores are always well stocked with ton of great cat toys, but they can be very expensive. Why pay money for toys when your cat will just as gladly play with something you got for free? Your kitty won't know the difference, but your pocket book will!
Cats love straws because they can be chased across the floor, carried in their mouths or chewed on. Especially for teething kittens, straws make great toys, and can be gotten free at a restaurant or fast food store.
Cardboard boxes make fantastic hiding places for cats. It's even better if there are holes in the box for them to stick their paws through or look out of. For kittens, pop boxes are the perfect size to sleep in, sit on and tumble around in.
Any type of small ball can be fun for a cat to play with, including Ping Pong balls, or pompoms from an old craft project. You can also make your own by rolling up a a bit of fabric (a child's sock would be perfect size). Cats also love tinfoil balls but don't let them play with them, as it's not good for their little teeth!
Of course this list would be incomplete without a mention of string. Why spend money on fancy chase toys when you cat would be just as happy with a spare piece of yarn or a shoelace? Drag it across the floor for them to chase, or tie it to a doorknob for them to bat at. Just make sure to put any small pieces of string out of reach if you're not supervising play time, because it can be dangerous if your cat decides to make a snack out of it.
This is obviously just a small sample of possibilities, there are tons of easy, free cat toys that you can make. Any thing that can be picked up, carried around or patted across the floor is game, and bonus points if it makes noise when it moves, just make sure it's big enough your kitty can't get it all in his mouth or it can pose a chocking hazard.