The R-09 uses standard SD flash memory cards (not the newer SDHC).

The largest SD card available today is 4GB.  The R-09 can't format the
4GB card, but if the card is formatted in a computer then the R-09 can
use its full capacity.

Owners report the Transcend 4GB and Adata 4GB SD cards work properly.
 The Patriot and PQI 4GB cards did not work after formatting in a PC.
(Incidentally, 4GB cards like the Transcend cost less than $60 these
days.)

Recording two channels at 24/48 to a 4GB card = 4 hours of tracks. 
Recording at 16/48 = 6 hours. The R-09 can capture this as a single
continuous recording if you need to. (Note, however, that many audio
editing programs have a file size limit of 2GB.)