After having a few high-gravity ales go nuts, I built one of these to keep my fermentation at a lower temperature:
I've tested it and it works great at all temperatures. I haven't really had to use it yet, though, living in california. my apartment stays at about 75, and the closet where i keep my brews is pretty steady between 68-73 lately. This summer it will get much hotter, though, and i'll get a chance to really see it in action.
Also, it doesn't do anything for heating...so don't know what to really do about those 55 degree nights, except keep it inside where it's warmer.