When working in Physics mode (or even in Arcade mode with a really brickish ship), it would be useful to have an accurate indicator of your ship's actual velocity direction. Perhaps a floating dot similar to the floating reticle of your nose indicator..

Perhaps four mid to dark blue hash marks, offset from the nose indicator so that it's visible when your nose and velocity direction match up.

Of course, it would be best if this was some form of toggle.

More thoughts on this one.. If your vector is currently behind you, out of your field of vision, you could put an 'inverse vector' in the field of vision, to show the direction you're coming from. The easiest way would probably be to change colors (red instead of blue? Might interfere with targeting reticle, tho..), but a change in graphic would also be good.

I've always just turned space junk up to high and used the debris to gauge my velocity. I figure it's artificial anyways, since open space shouldn't have that much junk in it (maybe that's what slows the ship when you stop turboing....)

And you have an absolute indicator of the magnitude of your velocity.. just not the direction - except for the debris.

This is an excellent idea.
It'll be 2 new things to measure around the radar in Hoax's HUD mockup. One guage for orientation up/down and another for orientation left/right
We just need one more.