Good Domain
At first blush, the Good Domain is kind of easy, but then again there aren't that many creatures that are just plain good, so I have to include LG and CG as options. I wanted at least three options for each spell level, so I had to give the Celestial template to ordinary good creatures in order to make them outsiders. And I wanted as many options for chaotic as lawful, so sometimes I had to include a suboptimal choice for balance.
Lesser Planar Ally (6HD or less)
-Celestial Giant Eagle (or Owl)
-Celestial Centaur
-Hound Archon (if lawful)
-Bralani (if chaotic)
(Any of these can be advanced to 6HD if desired, the Centaur can be given two ranger levels)
Planar Ally (12HD or less)
-Astral Deva
-Avoral
-Leonal
-Lammasu (if lawful)
-Trumpet Archon (if lawful)
-Coatl (if lawful)
-Ghaele (if chaotic)
-Lillend (if chaotic)
-Celestial Androsphinx (if chaotic)
(Any of these can be advanced to 12HD if desired)
Greater Planar Ally (18HD or less)
-Planetar*
-Huge (18HD) Avoral.
-Hound Archon Hero (if lawful)
-Huge (18HD) Lillend (if chaotic)
(Any of these can be advanced to 18HD if desired)
*The Planetar is troublesome even though it is within the spell HD limit, it can cast 9th level spells, so using an 8th level spell to get someone who can cast 9th level spells seems a bit out of wack.