We bought an old-fashioned (but new) Kirby about 10 years ago. It still vacuums just as well as it did when we bought it. It is a bit heav to lug up and down the stairs, but if you want something that lasts, well heavy usually means well-made in my book. We bought ours from a salesman that came to our door (like a couple of our neighbors- who are also very happy with their Kirbys), but I know you can buy them at some vacuum shops. Look up vacuum cleaners in your area. There are a couple shops in McKinney. I like Willett's.
I believe most or all of them have power assist- it drives forwards and backwards- much easier on the back (it's a heavy machine, remember).
You can check them out at http://www.kirby.com/Portals/0/index2.html. Guess you can request to have someone come to your house to demo it. It's going to be one of the more expensive vacuums- but usually things that last are more expensive. Ours has been worth it. Oh, and don't forget, if you have the demo and the guy starts making deals- negotiate, negotiate, negotiate. We got a good deal that way- better than others who don't negotiate well.