The uSD Platform Module is the cheapest way to connect a Micro SD card to the Propeller Platform, Protoboard, or breadboard. It comes on a tiny PCB, just 0.9" x 0.8" and includes pull-up resistors.

Usage with the Propeller is simple - just grab one of the SD Card objects from the Propeller Object exchange (John Twomey's library works well). If you mount it to connect through P0..P3, you'll just start fsrw with a mount(0).

With Arduino, you'll need a few more resistors to drop the Arduino's 5V logic to 3.3V. There's more information and libraries available on the Arduino forums.

The module comes pre-assembled, although you'll need to add 6 pin headers to the edge of the board to connect to a breadboard or Propeller Platform. Pin headers are included.