Many thanks to Beerrat for the heads-up on the Vassani. I purchased the same model for the same price at the local Home Depot and it is plenty big enough for a 6.5 gallon carboy. The unit fits nicely under my counter. It's pretty rudimentary, but at the "6" setting ("7" is the coldest), it chilled water down into the mid-40s. I brewed my first Kolsch this past Sunday, pitched two packets of Wyeast #2565 at 68 degrees F., and set the Vassani at "2". Twenty-four hours later, with a nice fermentation underway, the Kolsch was at 62 degrees F. By Tuesday morning, it was down to 60 degrees F. This morning, it was at 58 degrees F. I presume the temperature dropped slightly because the peak exothermic reaction has passed. So this morning, I set the dial midway between "1" and "2" because I want the fermentation back at 60 degrees F. Adding a temperature controller (as Beerrat did) would eliminate the guesswork on temperature settings but I think trial and error will be sufficient for my purposes.
It's much too soon to judge the unit, but I'm pleased so far and excited that I now have reasonable temperature control and much colder temperatures (than room temperature), if necessary, for fermenting my ales. The unit's "warmer" settings are in the low to mid-60s. Now I can brew sucessfully year-round here in DC, and I might even try a lager or two.
Thanks again, Beerrat!