Today I got an NCP1400 5V step-up board that takes any 1-4V source and ups it to 5V DC... Great for my supercap/solar PV cell power supply!
Also got the Sparkfun barometric pressure/temperature break out board BMP085
A little soldering of male headers and these boards are in action already! The pressure/temp board uses I2C, which is a bit more of a pain to code for than say analogue... However the example code gets the board up and running easily. Here's an example of the output in a spreadsheet...
The 5V step up board is great too - at the moment it's running from a dual-supply solar cell and supercap. The supercap is a bit underpowered, but a 60Watt lamp gives off enough juice to keep an LED going and charge the cap :)
##UPDATE - Got the 5V step up and 10F cap to power 'blink' sketch for about 2 minutes. Am now looking at low power methods with the ATMEGA chip so it wakes up, checks a sensor (stores the result) then drops to sleep again...