It would be easy if, when "mouselook" was turned off we could use the mouse to look and the arrow keys to turn. I usually fly in physics mode so quick checks are pretty easy for me. Just turn and adjust you acceleration based on where you are looking.

i suppose this has already been suggested, but if so, i don't know when and haven't seen the post.
now for the content:
what about adding the possibility of glancing quickly to your left, right, rear, above and below? the external camera moves just too slow to allow for a quick check. it could be put on the fkeys not in use by default, but linkable to whatever key you'd like, for lighting-fast accessibility ;)
also, VUDs would be nice, at least one, to have it display either your view of choice (rearview mirror of some kind) or (later on, hopefully) additional info on gizmos and outfits (think: comanche 3 by novalogic)

You can do it while using mouselook and turboing at the same time, because while you turbo, your direction is fixed, but you can still look around.

hmm...
yes, but the rearview mirror... on the other hand, i realize that that vdu (got the acronym wrong in the above post) would be too small to be able to show anything significant.
too bad

I want a button that frees up the viewing like boosting does, just without the boost. Easy as that.

Hold brake, s, and boost at the same time.

Turning your head in a cocpit would not cause the ship to change direction, loose power or speed up.