Joker, List,
Here is an excellent description of a home-built datalogger based around ATmega and SD card.
http://www.turtlesarehere.com/html/data_logger.html
It includes the code and the schematics/layout in Eagle format.
The hardware is simple to adapt from an Arduino.
The "Captain's Universe" is a good source for interfacing SD card to ATmega.
Happy New Year,
G