You are usually offered one with every purchase at a big-box store: an extended warranty. They are expensive and make you start to ponder whether you might need them. In fact, you don’t, especially because you can get it for free! How? With credit cards.
Plenty of cards feature extended warranties, that usually extend the manufacturer’s warranty by one year. For instance, most Visa Signature cards (including no-fee cards like the Chase Freedom Unlimited) have it, as well as some Amex cards and the Citi Prestige.
These credit card warranties are normally applied automatically to purchases you make with the card (at least when you buy at an authorized retailer). Therefore, there is really no reason to pay for this protection.
The only possible exception may be for mechanical items that tend to break down a lot (I’ve heard this is the case with treadmills, for example). There, it might make sense to spend the extra money in order to have the store come and repair the item if it breaks down. But, as a general rule, don’t waste your money!