I don’t normally worry about it except when the TR is on the couch, bed or other flexible surface—it heats up quickly.
My first solution was a plastic kitchen cutting board. Worked well, stable and non-slip.
I got the Cool-Lift from Handstands and sort of like it for the tilt it gives the keyboard. It is clearly best used on a desktop.
I recently picked up an Antec unit when Buy.com had it mispriced at $24. Haven’t had occasion to try it yet. I will most likely end up using this on my desk simply because I have it and the fans can’t do anything but help.
As for my couch-potato pad, I think I’ll pick up some stick-on feet from Radio Shack and put them on the cutting board to give the keyboard a little tilt.