I've got a pretty weird problem. I'm trying to interface to a microSD card using two of sparkfun's logic level changers: http://www.sparkfun.com/products/8745
I've got them set up like this:
Please excuse the horrid circuit diagram.
I've eliminated most of the obvious failure modes; drawing too much power from the arduino's 3.3v (powered it independantly from a 3.3v rail on an ATX PSU), pins plugged into the wrong place (checked four or five times) and basic electrical faults (half an hour with a multimeter). I've tried two different microSD cards that have been independantly verified as being A-OK, neither are kingston branded, and both were FAT32. I'm connecting to the microSD card via an SD-to-microSD adaptor. The adaptor works, I've measured all connections from the pads on the card.
I'm using the bog-standard SD card test sketch that comes with arduino 22. I'm using a 2560, the uno mega.