- 3d6 in order. Not for the faint of heart!
- For each ability score, roll 4d6(B3). That's 4d6, and keep the best 3. First determine all six ability scores in order, then feel free to swap around any two pairs of scores with their attributes. (That's as close as I feel like getting to "assign them at will.")
- The above method allocates a total of 24d6 to the six scores. When using the third method, however, one can distribute those 24 dice to the scores in any way the player wants -- as long as there are at least 3d6 for each score. Thus if you really want a fighter, go for it with 9d6(B3) for strength. But then you're stuck with just 3d6 for everything else. (With this method, there's no swapping when you're done.)
I calculated the probabilities using a simple script in IDL. If anyone is curious about extending the table in any way -- or seeing more significant figures! -- let me know and I can modify the script.