Any heightmap editors that know the heightfield is really on a sphere?

[Midgardsormr]

Mudbox and zBrush are 3d sculpting tools that actually go sort of in the other direction. Make the sphere, sculpt your terrain, then export the displacement map. Those programs, though, don't (as far as I am aware) have any erosion tools, so they're still not useful for your purpose.

[jezelf]

Are you trying to map and height map on a sphere without pinch distortion? Like needing Equirectangular height maps?

If so, there's this plugin for PS - Spherical Mapping Corrector by Richard Rosenman ( or at his website here )

You can also use panoramic photography tools which I've used before as a PS plugin to convert for cube maps for video games, which also converts different types of maps - but cant find the link atm.

there's also this Fixing your equirectangular poles

hope it helps