EmpireCovers makes protective covers for just about vehicle you'd want to shield from the elements: cars, trucks. SUVs , boats and motorcycles are all featured on their website. All of the covers they sell are fitted to a specific make and model. That gives them a superior fit but that level of specialization also makes them pricier than the discount covers you might find down at the discount store. Are they worth the extra cost?
I tested out an American Armor model cover for a Mazda Miata. That's the top end of the Empire line and they seem to be available for around $300 for most cars once you apply the available discounts.
At that price you get the Tyvek outer layer, the full elastic hem and a microfiber lining and a storage bag. The cover has stayed on through some intense GA storms and kept the car completely dry. The elastic hem makes a huge difference when you're trying to put the cover on and makes it an easy one-person job. Here's the best part: once you take the cover off, it's heavy enough that you can fold it by yourself for storage.
There's a 10-year warranty with this cover. Granted, most people store a car in a garage or a covered carport. If you do have to leave a car or (especially) a boat exposed to the elements, this is a top-quality option that's worth the investment.