We just picked up a super-cheap adjustable height laptop desk to test out as a standing desk, Scott. Something like
this. My husband is the product tester in chief, and so far, he's really happy with it.
In the past, we've used inflatibile exercise balls (like
this) as desk chairs, too. The challenge for me is that I'm fairly short, so if I get a ball big enough to reach my desk, my feet don't reach the floor (go ahead and laugh!) and I roll off the ball, but if I get a small enough ball, I can't reach my desk! Combining the exercise ball with a cheap adjustable desk looks like it's going to be a winning combination.
The great thing with the ball is you're always making slight adjustments to your balance, so it keeps you awake and alert. Active sitting.
My brother has a
swapper chair that he swears by but spending that much money isn't practical for me. You can find them in 'back stores' if you want to try one out sometime.
We've also tried
Kneeling chairs in the past, and while we liked the idea, the particular chairs we bought (not the chair in the link) were poor quality and broke fairly quickly.
The ultimate in standing desks would be a
treadputer. My husband desperately wants to build one but our circumstances aren't conducive (it's hard to put a treadmill in the Mini). We look forward to working our way up to a treadputer though.