I have about 10 games downloaded and still have around 1,000 blocks left, so a 2gig card will definitely hold you off for a while.
If you can afford it, try for the SanDisk Ultra II like what Joshieca has, they copy at like 66x or something like that as where a regular copies at 30x.. Isn't going to make much of a difference when transferring 1 game in and 1 game out, but if you're trying to move a lot of data at once then you'll appreciate the extra speed.