Well, first you taught your cat to Shake A Paw. And then you taught your cat to Sit up and Beg.
Now comes the trick that really drives the canines wild - Fetch!
I'll be honest with you. Not all cats will learn to fetch for you. It depends a bit on the personality of the individual cat.
Some will fetch... and some won't.
Certainly, there are some breeds that are renowned for fetching naturally. These include Siamese, Ragdolls, Abys and a lot more. But I have seen individual of all breeds fetch, including Persians and Exotics.
The Trick
To teach fetch, it helps if your cat has a bit of an oral fixation. It should like carrying things around in its mouth.
You might notice a kitten walking around with a toy in its mouth. Give it lots of praise!
Or another kitten playing with a ball on a string might grab the ball in its mouth and start to play tug of war with you - Let it win to reinforce it holding onto something in its mouth.
The Prop
You need a small and light-weight "ball" or object for your cat to fetch. Often, the best thing to start with is simple a crumpled up ball of paper. Soft sponge balls or even the sparkly crinkle balls also work well.
The toy must be something your cat is passionate about. :-) The more excited your cat is about the object, the more likely it is he will be likely to "grab" it in his mouth and carry it.
The Command
I use the verbal command "Fetch"... but you can choose any command you like.
The hand signal most often used is a simply pointing the finger or hand in the direction you have thrown the "ball".
The Reward
Unlike in teaching other tricks, a food reward is often not effective in encouraging a cat to fetch. The reward is that the object is thrown again to be fetched. The cat must enjoy the game of fetch - or else it will simply chase the ball without returning it to you.
Conclusion
If you notice one of your kitties carrying something in its mouth, it is a prime candidate for learning how to fetch. It is a trick that really impressed visitors - and it is a great way to give your cat extra exercise too!