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
$ iozone -e -I -a -s 50M -r 4k -r 512k -r 16M -i 0 -i 1 -i 2 | tee iozone_out.txt

I was reading the manual for iozone and it said to make sure, for accurate results, to make the -s switch size be TWICE your ram size. My Pi has 512mb so figured minus the 16mb gpu share I'd make it 1000M (for 1gb test file)

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

just apt-get install bonnie++ 

They claim it's often a power problem.

Forum user MrEngman reported some keyboard repeats and wireless hangs until upgrading to the debian6-19-04-2012 kernel, which he reports stable with no problems even with a low TP1-TP2 voltage of 4.65 - 4.68 volts.

Try plugging the keyboard and mouse directly into the Raspberry Pi, and see what happens.