Rare example of a human with a Breath Weapon, but no "taint": Fire Lad, of the Legion of Substitute Heroes, has the ability to breathe (and sneeze) fire. (Too bad he also has a raging set of allergies.)
Jack Kirby's Demon, Etrigan, breathes Hellfire from his mouth. It tends to function as normal, extremely hot fire, flames that burn one's soul, and infernal fires that destroy pure evil beings. It is of course, magical in nature.
Superman has arctic breath (essentially gusts of supercooled air which tend to freeze things in their path) and heat vision; as a counter to these, Bizarro has "freeze vision" and "heat breath", which is a nice way of saying that he breathes fire.
Superman (and, of course, all other Kryptonians and Daxamites) also possess hurricane breath; that is, they can create and direct gale-force winds simply by exhaling, without the winds necessarily being freezing cold. Pre-Crisis, Superman and Supergirl had such precise control over this power that it basically became telekinesis.
IDW's Transformers comics have featured Megatron, seemingly spontaneously, developing or formatting new abilities just because of the raw power at his disposal with Ore-13 ("ultra-energon"). Among these is a Breath Weapon.
Lesser known Batman villain Fright can exhale fear toxin.
Iron Man's rogue Fin Fang Foom is a fire breather of sorts. He blows out gas that can be ignited.
One of Richie Rich's enemies, the Onion, uses onion breath as his weapon, even making it powerful enough to destroy walls.
In similar vein, supervillian Superciuk note which means something like "Superdrunk" or maybe "Superalkie" from the Italian Alan Ford comics uses his high-proof breath to put his opponents into an alcoholic coma.
Doctor Doom in Ultimate Fantastic Four has the ability to exhale toxic/corrosive fumes as part of his transformation. Apparently, its based on the fact his now-useless organs were rotting into mush inside his body.