Did you ever try wxWidgets? The OSX support has come on leaps and bounds the last few dot releases.
I should take another look at it.
But in general it's pretty good. There was a GSOC project this year to implement a DirectX backend to the Windows drawing system instead of GDI but I don't know how well that has got on. They overhauled the drawing system to using native drawing contexts on whichever platform you're running, so you can do aliasing etc.
It's worth a look I think, as it is quite easy to write something usable in it very quickly. There is no database support anymore though - wxODBC died a death.