I was looking for quite a time to interface the SD card and avr’s in my projects, fortunately here is this demonstrative project which can be a good starting point for anybody who needs to store large amounts of data. By implementing the FAT32 file system the stored data can be accessed directly from any PC, without the micro controller interface. This is very useful since you don’t have to carry a laptop or the entire data logger around.
The project is well documented, it really gives the insight needed to understand the FAT32 system and how SD card work, the authors project has serial interface so the SD card can be accessed trough the Hyperterminal. The Atmega8 might be short in memory for the advanced FAT32 handling, so for the actual device it is recommended about 32K flash capacity controller.
Just imagine, instead of the I2C 32kbyte external eeprom you can have 1G storage capacity, and with the FAT32 system you won’t need the serial interface, usually used to download the stored data.
ATmega with SD card: [link]