1. Cats do not eat very much.
Cats are naturally grazing animals that eat small bits of food throughout the day (which is actually the healthiest way for a human to eat, as well). Their light diet and relatively cheap food will not be as hard on the pocketbook as a large dog or exotic pet.
2. Cats are usually not very loud.
Unless they're in heat (you should fix your cats, anyway) or stressed, cats tend to remain quiet. Sure, a dog can be somewhat trained to bark less, but such efforts are unnecessary with felines.
3. You don't have to worry about putting your cat out.
Cats come conveniently pre-programmed to use a litter box. Little to no training is required. With a cat, you'll never have to get up late at night for "business."
4. Cats are not as destructive as their reputation makes them seem.
True, cats do require something to scratch on, but very cheap scratching pads made of recycled cardboard are available. If you do get a habitually offending feline, train it just the same way you'd train a puppy not to eat your shoes. Squirt bottles are your best friend.
5. Cats do not need as much attention as other pets.
Most felines are solitary by nature. While a dog or ferret will greatly suffer from lack of social play, cats are perfectly content to keep themselves entertained. Granted, you still may get the occasional cuddle bug. If you want multiple cats, make sure they grow up together for the best chances of them getting along.
6. Cats are actually compatible with other pets.
Cats and dogs are notorious for not getting along; however, cats are likely to get along with any other animals that they are raised around. This also applies to them getting along with other felines.
7. There are many types of cats.
Most people freak out over dog breeds, but simply think of cats as cats. This is illustrated by the following:
There are actually several different breeds of domestic cats. There are even cats with naturally low allergens.
8. You can be a dog person and not hate cats!
I don't know why people think that liking dogs and liking cats are mutually exclusive. It must go back to the whole "dogs and cats can never get along" myth. As a cat person, I still love dogs. It's just like Kristin Chenoweth said: "You can love animals and still eat meat! It's allowed!" You can like dogs AND like cats, I promise.
I hope you now see that cats are viable best friends, even if you love dogs. They're low maintenance and extremely adorable. Trust me, you'll at least want one when you get old and have empty nest syndrome. If you're deathly allergic, I apologize for your sad, depraved life without cats. Try looking into an allergy friendly one, please. Cats can make your life so much better.