I've also had luck with 3.5" HD enclosures, they were as cheap as the drive without enclosure and with a bit creativity make for very nice looking enclosures for electronic projects.

Another pro-tip I picked up is using match-boxes for storing electronics (resistors, connectors, small modules). They are cheap and you can tape/glue them together to create arrays of small boxes. The sides are clear thus perfect to write what they contain.