Open Source Data Logger Project Using the Arduino?

Hello,
I have a need for a different type of data logger. I want to log incoming ASCII serial data to an SD card. I also want to send commands to the attached instrument. I'm thinking that I can use the Adafruit GPS/SD logger shield, but rather than a GPS, I'll attach my device (an ADCP). I haven't found any simpler or cheaper SD card shields.

I'm in the fortunate position of having plenty of (solar) power available, but I have some other applications where this may not be the case.

This could also be used to add memory to instruments where memory upgrades are either unavailable or expensive using the serial output.

There are devices such as the logomatic from sparkfun which comes close, but I'd like to build this around an arduino. I'd also like to use a FAT16 or even FAT32 formatted card. Unless I'm mistaken (which is probable) this shouldn't be too hard to do, especially with an Atmega328.

-RyanN