There are two that I know of: 1) The Yogourmet, which is electric and heats the temperature gradually to 112 degrees F so that you can make probiotic yogurt. It takes 12 hours to make yogurt. I don't have this one, but I'm considering buying it. 2) The Yogotherm, which is non-electric. Basically it is a 2 liter (or 2 quart) plastic bucket that fits snugly inside of a styrofoan shell. It also takes about 12 hours to make yogurt. I have owned one of these for about 7 or 8 years and I like it very much. The only thing about using this one is you have to careful and watch the milk as it cools so you can catch at the right temperature. This isn't very hard, but you must be around the house for the 1-2 hours that it takes to cool. Also, you can make less than 2 quarts if you want.
Thank you, D. Knight. I like what I have read about the Salton YM9 1-qt yogurt maker, but would buy a 2 or even 3 quart unit from them in a hurry. The Yogourmet costs $65 on Amazon, it would be better to buy two YM9's from Salton for $20!
Checkout http://www.dairyconnection.com. They sell the Yogotherm and replacement pails and lids. I use their Aby-2c culture to make the most amazing yogurt. I have had very fast shipping and great service from them.
Google will turn up a couple of other places, too, but look to be more $.