Antlinux

I found this project on InventGeek about how to build an alpha radiation visualizer. The alpha radiation coming from a smoke detector emitter element hits the CCD of a USB webcam in "random order", thereby creating entropy!

The above links describe the project from start to finish, including materials and construction hints.

If you do decide to build this, you can install the rng-tools
package (Debian versions of the packages) in order to read in the data being sent from the camera and send that to the kernel's PRNG device in order to 'stir up' the kernel's entropy pool.