[beardicus]

I'm most interested in the JeeNode, which can be found yonder:

http://jeelabs.net/projects/hardware/wiki/JeeNode

They're basically a stripped down older Arduino (none of the built in USB or other new features of the newer Arduinos) with built in wireless (433 or 915mhz depending on your region), and the developer has done a ton of work getting them to be incredibly low power, mostly by working around some decisions made in the core Arduino libraries. He has had some running off of coin cells doing a test ping routine for more than a year now, if I recall correctly.

You'd need a gateway of some sort to get the data onto the internet proper, of course, but he also makes a usb dongle with the appropriate receiver, which you could plug into a raspberry pi or even a wifi router that supports USB serial devices.