ways to modify breath weapons?

[CyberThread]

Besides feats, what can modify a breath weapon

[Unbalanced]

Spells:
Breath Weapon Admixture - Transmutation - found in Draconomicon
Breath Weapon Substitution - Transmutation - found in Draconomicon

[MesiDoomstalker]

There are a whole slew of them in the Spell Compendium. My favorite is Enervating Breath, a 9th level Sor/Wiz spell. It basically turns your Breath Weapon into a AoE Enervation, but all the benefits of having it as a spell.

[Pluto!]

The Dragon Spirit Cincture from the MIC adds one die and can add 1 to the DC.

And a bunch of spells in the Draconomicon and SpC that do things like add blinding rider effects to breath weapons or animate breath as elementals.

I don't have MoI, but it's one of the places I'd look, just on the off-chance that its breath weapon soulmelds are phrased in such a way that their essentia investments affect other sources of breath weapon (assuming this thread is also along the Dragonborn train of thought).

[Chronos]

Unfortunately, the breath weapon soulmelds aren't even technically described as breath weapons at all.

[MesiDoomstalker]

I found an old thread (http://www.giantitp.com/forums/showthread.php?t=220697)of mine about a Breath Weapon focused character, it should be of some use.