any 150x card, as long as it's not a fake, all brand names usually work the same.
I would look at FRY's, you can get a 2gb for 7.99 USD if it's on sale (fry's are only in America)
150x 4gb, I got a transend like this for $60..
for general usage I have a "normal" (no sure how many x..) 4gb card..
the only real performance boost I found was gngeo2x
I have use:
sandisk
kingston
corsair
and
transend cards, all of them work fine on the 2x