From
Wikipedia:
The original XD cards were available in 16 MB—512 MB capacities.
As of August 2006, Type M cards are available in sizes from 256 MB to 2 GB. However, the Type M suffers slower read-write speeds than the original cards.
The Type H card offers higher data rates than Type M cards (theoretically as much as 3 times faster). As of 2006, Type H cards are only available in 256MB, 512 MB and 1 GB capacities.
Compatibility lists are available for
Olympus (PDF format) and
Fujifilm
RC