SdFat has a soft SPI mode and I wrote soft I2C libraries so the AdaFruit Shield can be used on Mega, Leonardo, and 328 Arduinos.
Here is an example sketch and the libraries - AdafruitLogger20121219.zip Google Code Archive - Long-term storage for Google Code Project Hosting..
The previous version plus this version of the sketch and libraries have been downloaded over 1000 times.