Not a steamer but the model I have - the ProHeat one - heats the liquid and it seems to work well.
My sense is that it works well for the price. I think I got it for around $70.
EDIT:
- What I like about it: You can spray the heated liquid detergent onto the carpet (as much as you want) and then brush it in as much as you want. (I like being able to work it in with lots of liquid and heat.) Then you can suck the carpet dry with the suction in the turbo brush. The machine is also well designed and easy to clean (including the brushes)
- What isn't practical about it: You need smaller brushes for the crevices/ smaller areas.
Does anyone know of a high quality steamer that isn't too expensive?