When building your own internet enabled device it helps if you can use a platform that already has web-connectivity built in. The Nanode is exactly this. Based on the wildly popular Arduino form factor it allows you to use arduino shields for you device. The Nanode has an onboard ethernet jack so makes it easy to connect you device to the internet. All software and hardware is open-source so you can modify ‘everything’ to your harts desire. The Nanode comes already in a number of flavors (adding 868Mhz RF for instance) so you already have a lot of different options with this platform.
The Nanode is not carried by any electronics vendor that I know of, so availability might be a problem. If you want one you can contact @monsonite on twitter. Update: I see on the Nanode website that they plan to open an online store in january 2012, so you may buy one http://www.nanode.eu/buy
I have not used the nanode in any project (yet). I would like to get my hands on one though. I espescially like the compatibility between the Nanode and the Jeenode http://jeenode.com. At 250mA the Nanode is a great low-power always-on platform for your device (If anyone can confirm these energy consumption specs, I would be very interested to hear their results).