More examples!
If you want to use an SD card for datalogging, we suggest checking out our Datalogging shield and GPS logging shield - there's example code specifically for those purposes.
If you want to use the SD card for loading images (such as for a color display) look at our 2.8" TFT shield and 1.8" TFT breakout tutorials. Those have examples of how we read BMP files off disk and parse them.