Random
From Hackepedia
Randomness in some UNIX operating system can be achieved through cryptographically achieved randomness such as arc4random(3) which uses the interfaces /dev/random, /dev/arandom and /dev/urandom. This method is assumed to be pretty good, more on this at RFC 4086. Weak randomness can often lead to a system compromise.
Entropy sources
Sound cards and their white noise are a good means of entropy. Some CPU's provide random number generators which the Operating System may use. Crypto-accelerating cards usually provide a source of entropy.
