SD cards seem to be available up to 2GB. CF cards seem to be available up to 8GB, although I would hesitate to put so much data onto one card. They all come in different flavours of read/write enhancement. If you are pondering this question in relation to a Canon 1D/1DS MKII and are planning to use the excellent Epson P-2000 as a storage device, it is as well to be aware that the P-2000 does not support SD cards larger than 1GB.