I talked about randomizing the breath weapons in that post: "One way to do this is to roll on the 20-sided Geography table -- yes, the Geography table! -- for the terrain modifier or alternatively the event. That gives you 14 possible breath weapons." This, of course, is only the beginning, since you could opt to roll 2d20 instead and use the formula Modifier X + Event Y, or even read one of the results off the main or exotic table instead. This gives 196 breath weapons -- more, actually, not just because of the freedom of interpretation, but also because of the trick of reading the dice differently if they overlap horizontally.
If you don't want to always roll 2d20, you could roll a d6 first to determine breath weapon variety: 1 = no breath weapon, 2-5 = roll 1d20 on table, 6 = roll 2d20 on table. In fact, here are some other d6 variety rolls for dragons:
- Legs: 1 = no legs, 2 = bipedal, 3-5 = quadrupedal, 6 = centipedal
- Wings: 1-4 = no wings, 5-6 = wings
- Tail: 1 = prehensile, 2-5 = armored, 6 = stinger
- Size: 1 = small (rhino-sized) 2-4 = medium (elephant-sized) 5 = large (brontosaur-sized) 6 = gargantuan (mountain-sized)