Network-enabled thermostat?

There are a number of options available, this thread on another forum gives you some indication of your options - do look around the rest of that forum since it's entirely about home automation.

Once you've chosen a product you'll need to configure an update client, forward the relevant ports and test remotely, all covered in this answer. Anything that has a web interface will almost certainly use 80/TCP, the default HTTP port.

There are also services like AlertMe where the control panel is on the web.

Try http://www.proliphix.com/. they also sell them on http://homeautomation.com. Work great. I have 2 at a vacation home. Free dyndns and alerting support.

Hi, I am just adding such a system to my vacation property, it uses an OMNISTAT 2 thermostat and a small emmbedded computer to update a website, it aslo will allow me to change settings and switch OFF/ON X10 devices.

You can view the live test page at http://www.designservicesonline.com/test.php

but be aware that it may stop working or show odd results as I am still working on it.

Regards, Bill

I helped somebody install one made by ControlByWeb.com called the X-300.

So far so good.

By far, the best one I've seen is the one I own -- Ecobee. Check out http://www.ecobee.com -- it's a color LCD touchscreen and allows programming via local or remote from any web browser. It features a web portal and automatically tunnels, so you don't need to open any special ports on your router or WAP or configure any clients, etc as mentioned in the previous answer -- truly set it and forget it. You can control all aspects of the stat remotely, even turning the system on or off in case you forgot before going on a trip. You can schedule vacations so the house is comfortable when you return. There are even some external dry contact inputs with customizable text that you can interface with your security system or anything else that has a relay output. I have one of my inputs tied to a whole house water leak detection system, so any time it activates, the stat displays a time stamped alert screen and sends an email that I receive on my Blackberry. It also has real-time weather forecasts built in and charts system activity (indoor, outdoor temps, humidity, set points, fan activity, etc.) It retails for $469 but that includes lifetime web portal (I think I paid $399 a couple years ago, but at the time, the remote subscription was going to run $35/yr). The slightly higher price might also signal a new version as I see that they are taking pre-orders to ship in March, 2010. I would definitely purchase another one in a heartbeat...