Tammy, we have had our True treadmill since 1999 and it is used regularly by DH and myself and an occaisional teenager. It has held up well, and it has a joint friendly surface.
www.treadmilldoctor.com - they fix treadmills so have a good idea what stands up to the test and what doesn't. But I know from reading these forums that a lot of people have good treadmills that the treadmill dr. will tell you are junk. It's just nice to have an outside opinion from a company not connected with the sales.
I found this site very useful when searching for information about different types of treadmills. They represent all different manufacturer's and price ranges. www.treadmilladviser.com