Here are a few styles. I have a really crummy 15 year old beat-up one from Harbor Freight. I also have some old rolling desk chairs that I took the arms and back off of.
I have one of those too... Better cushion, the caster castle nuts don't come off all the time, but it doesn't have that handy catch tray on the bottom or the adjustable seat shock
I really like that seat height adjustment.
