In linux, the interface is /dev/(u)random. Many crypto software use it. check http://en.wikipedia.org/wiki//dev/random

the following command gives 64 bytes of random data:

[atp@risci1 ~]$ dd if=/dev/urandom bs=64 count=1 | od
1+0 records in
1+0 records out
64 bytes (64 B) copied, 6.0784e-05 seconds, 1.1 MB/s
0000000 125047 155010 151240 044101 134716 055204 027564 056065
0000020 000400 167744 111504 136012 136674 175425 045721 005465
0000040 111165 146462 106526 175406 153705 053636 101666 057700
0000060 175272 161005 105256 053347 171741 072074 127474 042150

Nowadays, the chip is built in almost all motherboard. This link is better. http://en.wikipedia.org/wiki/Hardware_random_number_generator

I remember there are also RNG using photon or other quantum stuff. They are not very expensive (price comparable to harddisk, I think), easy to use and not very big in size. Dr Chang Ee Chien mentioned it on his crypto class.