Just this cheap Amazon one.
I use that for my Xbox to HD CRT because Xbox runs in 1080p but the tv is only 1080i. And the converter can alter the resolution with a click of a button.
Otherwise, for my computer to HD CRT or even Xbox to CRT monitor, I use the excellent HD Fury Pro 2. It cannot change the resolution itself but, as long as you don't need that capability, the quality is amazing. It can convert HDMI to component or VGA. Xbox games look fantastic running 1080p on the monitor. And my computer can natively output 1080i so media looks great on my HD CRT.
There is another option , about half the price with no upscaler.