random.org 

Random.org offers true random numbers to anyone on the internet.

http://www.random.org/ 

hoW?
The easiest way is to use a web form to generate random integers (with duplicates, like dice rolls), randomized sequences (without duplicates, like lottery tickets) or raw random bytes. You can also flip virtual coins and generate random bitmaps.

[+ info :  «introduction to randomness and random numbers»]

[..] The idea of using atmospheric noise to generate random numbers came up when some friends and I were building a prototype of an online gambling system. Using noise in this way isn’t a particularly original idea, though. Other people thought of it before us, and as mentioned above, there are already several public random number services out there, some of which use more advanced methods. So, why yet another? The most important reason is because it was fun to make. The second most important reason is that existing services are mostly for educative purposes – and for fun! I hope random.org will prove itself informative and fun but also useful for certain (non-critical) applications that need random numbers. Random.org is the only service I know of which offers a large (16K) block of numbers at once and which has a CORBA interface.

The way the random.org random number generator works is quite simple. A radio is tuned into a frequency where nobody is broadcasting. The atmospheric noise picked up by the receiver is fed into a Sun SPARC workstation through the microphone port where it is sampled by a program as an eight bit mono signal at a frequency of 8KHz. The upper seven bits of each sample are discarded immediately and the remaining bits are gathered and turned into a stream of bits with a high content of entropy. Skew correction is performed on the bit stream, in order to ensure that there is an approximately even distribution of 0s and 1s […]

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and for non-random numbers:

http://www.noentropy.net 
: :: ::: Your online source for truly deterministic numbers

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