We have a Sleep Number bed. Both Kevin and I just love it. Before, we had a foam memory topper and 6 egg crates on top of that on top of an older mattress, which is ok, but still not as soft as a Sleep Number bed. I still have one egg crate mattress topper on top of the Sleep Number bed - I think it helps smooth it out. My only peeve is that when he is not in the bed, it tends to roll me to the middle of the bed.
Here's some info on Sleep Number beds:
There are two outlets in Texas that I know of, if you know of another one, let me know.
interesting forum discussion:
The Radisson hotel chain has quite a lot of Sleep Number beds - you can stay the night at one of them to check it out.
same with tempurpedic
While looking up all this stuff, I found this site to be intriguing.