Just about everyone needs to use a cat carrier at some point in their time owning a cat. This may be to take them to the vet, to take them to be boarded, or if you are moving house. It is not generally a good idea to let your cat run loose in a car, no matter how well-behaved they are.
There are many different types of cat carriers available. The cheapest ones are simply made from cardboard! These are made to only be used once and are generally only recommended for small kittens. Most big cats will either be too heavy for the cardboard, or will scratch/chew through it.
I think the moderately priced cat carriers are generally the most appropriate for most people. These are ones which are made from a high quality hard plastic or soft fabric. These are well-made, and can carry a larger cat (15+ pounds), and do not hurt your hand while you carry them. It is up to you whether you prefer a soft carrier or a hard plastic carrier.
If you are carrying the carrier quite far, you may wish to buy one which has wheels, much like wheeled luggage, as this makes it easier to transport. If you are traveling by plane with the cat, I recommend a climate-controlled carrier. These are much more expensive, but many cats have become ill or even died from being held in cargo holds which do not have heat. If you need to fly with your cat, I highly recommend this.
For other long travels, you will want to make sure that the carrier has room for a food and water bowl. This way the cat can eat at his leisure. You may also want to put in a puppy wee-wee pad, since the cat may not be able to use the litter box for some time. I always put in a towel or old blanket as well, this helps the cat stay warm if he becomes cold. I also make sure that the blanket carries my smell or the cat's smell, to make it more comforting.
Remember that traveling is very stressful for your cat. You will want to do everything you can to make it as easy as possible for him. Make sure that he is comfortable and well fed. In the car, talk soothingly to the cat, it will calm him down hearing your voice.
