As I recall (dimly) some of the early computers actually used
background radiation to seed their random number generators, although the
random number generators in use at the time were pretty non-random.
Unfortunately, many of those old routines have found their way into some of
the "built-in" random number generators in a number of compilers. However,
there are a number of "portable" random number generators that are quite a
bit better. "Numerical Recipes" has a good discussion of random number
generators, and code for several decent "portable" random number generators.