Kirby Vacuum Cleaners
Kirby make a very durable vacuum cleaner. They are also very expensive, so if you want a to buy a Kirby or already own one, you need to be a careful of what you actually vacuum off the floor. Take reasonably good care of your Kirby vacuum cleaner and it will can last you 2 or 3 times longer than most residental vacuum cleaners.
Most of the recent Kirby vacuum cleaners have a plastic fan. You can verify this by searching for Kirby fan replacement kits. All plastic. Kirby doesn't utilize a bypass system like a canister does. This means you can screw up this big, heavy, hulking machine very easily. Plastic fans can break when you pick up hard objects or can become jammed, putting unneeded stress on your Kirby vacuum.
Kirby vacuum cleaners last a long time because they don't fall apart or wear over time like it's plastic covered competitors. With the exception of the fan, the vacuum is really durable from top to bottom, but new ones cost about as much as a central vacuum cleaner system.
If I was going to buy a Kirby, I would look for a used or rebuilt one, unless you can afford a new one. It's a lot easier to validate the cost of a new or used Kirby vacuum if you plan on using it to shampoo carpets. I have customers who lug this vacuum to small offices they clean, and they get paid pretty well for it. If you have a two story home, I wouldn't recommend buying a Kirby (yes, they are that heavy).
If you have a Kirby Generation (3 thru 7), an Ultimate G series, Sentria, or basically any Kirby that uses some kind of vacuum cleaner bag that has a round whole (Yes, this includes Kirby vacuum cleaner that use a Style 3 bag, like the Heritage II, or the Legends), spend some money and get the new HEPA Kirby vacuum cleaner bags. These filter bags are not limited to the Sentria (they fit all Kirby vacuums made the last 20 years (except the 2009 Sentria). They are white and feel like cloth. They are more resistant to tears, and really do a great job of filtering the debris that enters the vacuum bag area. More and more vacuum cleaner manufacturers are going or have already gone to this "cloth-like" style of dust bag.
Finally, change the vacuum belt every year. Don't wait for it to break. Kirby belts stretch. As they stretch, your $600 to $2000 investments becomes a less effective cleaner because you haven't replaced a part that cost under 3 dollars, and couldn't be easier to buy on the internet (all Kirby vacuum cleaners use the same size belt).