New Arduino form factor
A couple of new versions of Arduino boards can be found on Arduino blog: the Arduino Pro and the Arduino Pro Mini (depicted here). Both work at 3.3V and I think that makes them ideal for battery-powered applications.
In my case I'm going to create a small circuit to interface the Mini to an XBee wireless module to create a smallish wireless sensor. Hopefully I'll get much longer operation times than those Rob Faludi measured with Diecimila and XBee shield.