Polygonal Labs has an excellent random number generator. There is an AS2 and AS3 version and it has much better random numbers tools such as seeds and ranges.
When developing games you often need a PRNG that, once initialized with a seed value, produces always the same sequence of random numbers after it. The Math.rand() function in Flash is a PRNG, but it doesn’t let you define a seed value (I think it’s picked randomly when the swf starts, but there isn’t much information about it) so another solution has to be found.
One of the best PRNGs is the Mersenne Twister algorithm, but in my opinion it’s total overkill for flash games (also slow and difficult to implement). However, after spending some time with google I found an interesting site explaining the implementation of the Park-Miller-Carta PRNG, which belongs to the group of Linear congruential generators (LCGs).
Download & Usage
First define a seed value (default is one) and then call nextInt() to get the next integer value, nextDouble() to get a floating point number between 0..1 and nextIntRange() or nextDoubleRange() to generate numbers within a certain range.