The Mersenne Twister is a fast, efficient pseudorandom number generator with a very long period. It is not secure enough for cryptographical uses, but is more than adequate for computer games. Due to it's speed and effective generation of psuedorandom numbers, a few languages (for example FreePascal) have already begun using the Mersenne Twister as its default algorithm for its own RNG.
The original C source for the MT: MT Source
The official webpage of the MT: Mersenne Twister Homepage