We bought one of these about 4 years ago:
http://www.thermostatshop.com/cem24-series.shtml.
It's a "talking thermostat" that lets you check conditions at the remote house, raise and lower the temperature, etc. It worked so well that we bought a second one for our primary residence.
I would note that the manual was not that easy to understand. And I would agree that having a professional HVAC guy install it is probably the way to go. I did it myself, and it took a fair amount of hand-holding to get things working right.
The model we bought did not have the built-in freeze alarm. I don't think it was offered at that time. So when we went south for the winter this year, we supplemented the thermostat with one of these:
http://www.smarthome.com/7001.html
I liked this one a lot. Very easy to install and program.
But if you want the whole combination of remote-control thermostat plus freeze alarm, it's probably cheaper and easier to get one unit that does everything.