I have been using 32GB cards from Transcend (currently worth 65US$) on a D3/D3x for more than one year and have had no problem whatsoever.
They are a bit slow compared to the fastest cards, but still good enough, not sure why anyone but sport folks need to spend 10 times the price on Sandisk or other brands. I guess that the double CF slot of the Nikons in back up mode helps here though.
Cheers,
Bernard