FAT12/16/32, AVR/C (& Linux), but maybe useful: http://www.sf.net/projects/efsl

And a couple of random thoughts:
- SD requires far less lines than CF (for which some means of IO expansion is often inevitable
- speed is not a typical issue with '51, so those arguments are off
- full SD specs are AFAIK not public
- beware, we have seen of some CF not implementing 8-bit mode properly
- we have seen erratic behaviour of some CFs when the reset was not long enough
- FAT would require some 512B-1kB of RAM buffer
- if you need read only, you don't need a full FAT implementation and also th memory requirement may be much lower
- Jez is (partially) right, search this forum for discussion on FAT
- somebody should write a FAQ... (or a wiki article? :-)

Jan Waclawek