I'd have to say that the 3.5" enclosures have become obsolete. They use a normal desktop-size hard drive (which are cheap, I admit) but are big, heavy, and require a seperate power adapter plugged into an AC outlet.
Now that 2.5" notebook drives have gotten a lot cheaper, the 2.5" external enclosures are the way to go. They are way smaller than the size implies, and are powered from the USB2 port. Better yet, because they don't need a separate AC adapter, the 2.5" enclosures cost a lot less then the 3.5". I like this one a lot, and it's $8.99 with free shipping!
http://www.pcmicrostore.com/PartDetail. ... p:10501713
Get a bigger drive for your notebook, and put the old one from the notebook in your enclosure. You can get a 2.5" 60GB for $85 or so, and an 80 for around $100. Try the 2.5" external, and you'll never go back.