Can't find a Half-Deity type template.

[Alzrius]

If you're partial to third-party products, you could use the Divinely-Infused Creature template, from Malhaoc Press's Requiem for a God. The template is made for a creature that gained energy from a god's death, but it could work just a well for the child of a god and a mortal.

 

[Viktyr Gehrig]

I'd use whichever half-outsider (or half-elemental) template is most appropriate for the deific parent. If the story requires that the creature in question have human (or normal humanoid) physical appearance, I'd remove wings, natural weapons, and such, and lower the LA by one.

 

[Angel Tarragon]

Wouldn't Mongoose's Book of Immortals have such a thing?