Really cheap flash memory
At your local Micro Center, behind the counter, they have USB flash-memory sticks for $16 for 2 GB.
There is a catch: It comes with a second read-only memory device containing preinstalled software for Windows. Fortunately, this is easy to disable with a simple fstab rule.
The main storage device, on the other hand, is easily reformatted in Disk Utility. The stick is USB 2.0, as you can see from my dd results:
Plugged into my keyboard (thereby constrained to USB 1.1)
dd bs=62914560 count=1 if=/dev/zero of=temp %/Volumes/Stick of data(0) 1+0 records in 1+0 records out 62914560 bytes transferred in 63.105605 secs (996973 bytes/sec)
Plugged directly into one of my USB 2.0 ports
dd bs=62914560 count=1 if=/dev/zero of=temp %/Volumes/Stick of data(0) 1+0 records in 1+0 records out 62914560 bytes transferred in 11.250311 secs (5592251 bytes/sec)
In case you’re wondering, 62,914,560 bytes is 480 megabits, the theoretical maximum throughput of USB 2.0. If I were using 100% of that bandwidth, the write would have happened in one second. As it was, the write did about 5+⅓ MiB per second over USB 2.0, and 19⁄20 MiB per second over USB 1.1.
Pretty good for $16, I think.
UPDATE 2008-11-29: Sometime in the last few months, Micro Center reorganized the front of their store. Now, the cheap store-brand flash memory is in racks right there on the counter.
And prices have come down even further, of course. Now, 4 GiB will cost you $10. And they no longer limit you to USB thumb drives: they now offer SD cards, as well.