We’re using the random object for many things, by its nature it may repeat a number, but sometimes we don’t want to get the same number more than once, for example when showing a random image out of an array of images, or jumping to a random frame in a MovieClip. Currently there is no ‘unique’ function in Actionscript, you have to write your own solution.
Here is my class for generating random numbers:

Download: RandomPlus.as.
Usage:
Create an instance of RandomPlus, defining the numbers scope (start & end numbers), including negative values. in case only one parameter is passed the RandomPlus object will assume it is the end number and that the start number is zero:
var rp:RandomPlus = new RandomPlus( end:Number, start:Number = 0 );
After that you can use ‘getNum’ public function that will return a random number within the scope:
rp.getNum(); // returns a Number
You can use public var ‘len’ to retrieve the length of the scope in case you want to use it for your function:
rp.len; // returns a Number
*The object will return unlimited amount of numbers, each time the entire scope was returned it will reshuffle the items so it will continue to return random numbers within the scope, in an ever-changing order.
Let me know if you liked it (or if you have suggestions), enjoy :)