Bitcoin-QT: which external memory (connected via USB2.0 + TrueCrypt) would work?
The cheapest external memory that would work fast enough to be acceptable is SATA3 HDD via usb2.0 adapter. (I didn't tested SATA1 or 2 nor old IDE drives, if you have them with over 500GB capacity you can probably use them too. I couldn't find them for my test).
For comparison, here's the time was needed to import 21GB blockchain:


2.0 USB flashdrive: never finished. took 7 days non-stop for progress bar to reach 1/3. and then speed slowed down to the point that there was no noticeable progress.
SATA3 HDD via USB2.0 adapter: about 20 hours non-stop.