Q234: What are some good 1-10HD outsiders to become/own if you have access to all spells & abilities? (No I'm not asking for Planar Shepard abuse...)
Nightmare (Astral Projection, Etherealness),
Couatl (9th level sorcerer, tons of other awesome stuff), Succubus (Etherealness, Change Shape), Hound Archon (PfE aura, Greater Teleport at will). Also look through the Summoner's Guide to the Lower Planes. I found it very informative. He even has information in there on all kinds of things that would be difficult to summon (outside of Gate, Planar Binding, etc).
Too bad the Astral Deva is just outside that range. 14th level cleric casting would be nice.
There are other kinds of devas in the splatbooks, and I'm sure there are probably some that fall under the 10 HD limit, though.