I honestly don't know about the general opinion on these, but we have started using one of the ultrasonic noise things for when are dogs bark outside (the neighbors pull up at all hours of the night, starting both dogs on a barking attack) Anyway, it really has worked wonders for the last couple weeks. We'll still get little yips, but it usually calms them down after a couple of barks.
This is the one we have:
The Ultrasonic Barking Dog Deterrent at Hammacher Schlemmer