Last year I was looking for such a device to allow me to montitor my speed more easily on approach so I didn't have to glance at the panel during this critical stage of flight. I found this affordable, small box that plumbs into your pitot line and runs on 12V. It is made in England. I only turn it on for landing so I added a power switch. It is made for headphone use so I added a small amplifier circuit to drive a speaker.(Will supply schematic if you want it.) I am pretty happy with it and thought others might like to know about it. This device should really help pilots avoid the stall-spin on approach problem as well as achieving a low-energy touchdown.
Link: http://www.smartavionics.com/prod-smartass.html