Even though we all use the Kingston cards with success, I have read on the Oade board that they are still not a preffered card, nor are they on the Marantz recomended list.
Sandisc is solid. And I dont believe that speed will equal anything other than batteries that draining faster when we are talking about 16bit recording w/the 660. So just go cheap, and you'll be fine. Several 2gbs, a 4gb..shit, i'd even run a microdrive in one of those suckers, though that will certainly affect the battery life.
Then agaian, with 7 hour runtimes on good nimh AAs, who cares.
Just dont cheap out and get some noname ass brand. that will certainly not work.
Lexar is another on the list.