From this thread on SD cards, the comment from by carlosfm on Mon Aug 27, 2012 9:46 pm suggests that the 16GB Sandisk Extreme Class 10 45MB/s working fine on my Pi might be a good card to use.

Partway down the page, it says there's a debian package to download:

$ wget https://dl.dropbox.com/u/15710882/iozone3_397-2_armhf.deb
$ sudo dpkg -i iozone3_397-2_armhf.deb

Still, there's more to learn. Something about:

just apt-get install bonnie++