I just picked up one of these to hold all my virtual machines:
Wester Digital Passport
I spend a lot of time on three different machines (home, work, and laptop), and I was having a difficult time working through lab exercises across all of these machines. This has allowed me to keep working with the same setup regardless of where I am. I picked up an open-box 120gb version for $70. That gives me more than enough room for all my VMs, TechNet ISOs, etc.
It comes with a really short cord, scratches/smudges easily, and 5400rpm is a tad on the slow side. I'm not using it for video editing, and I picked up Case Logic case from Amazon for around $15. I'd recommend this (or something similar) for people who spend a lot of time studying in various places.