From the Marantz site:
PMD671 Operational Questions
What kind of media is recommended?
Depending on your application, you'll want to select a proper compact flash type I or type II, or microdrive memory card to use with your PMD671 solid state recorder. Typically standard cards with faster read/write speeds are best. You'll want to stay away from cards marked as "ultra" or anything else other than standard. If your application is one where the machine is constantly moving or subject to vibration, then you should buy a compact flash card as opposed to a microdrive.
Some recommended brands of flash cards are: Lexar, Viking, Hitachi, IBM, and PNY.
FWIW, I bought the 4 GB Kingston Elite on Doug Oade's recommendation. When I e-mailed Marantz about the Kingston, they told me it was probably OK to use, but still not on their recommended list. I have had no problems with it so far.