Cubemaps are becoming usable on graphics hardware. NVIDIA is supporting them, at least. Also, games like Quake and Halflife use cube-based skies. (You draw a huge cube instead of clearing the screen, and then just draw with the 3x3 submatrix of the current modelview, which means you ignore translation.)
Sample output from this Bryce scene.
Bryce 4 can do animation. I (ab)used that ability to create an "animation" that really just outputs 6 faces of a cubemap by animating the camera.
Bryce's renderer takes some liberties with reality, including multiplying the FOV by 80%, so you have to actually know a little bit about how the program works to make this animation work well.
To use it, load the animation, choose a sky, uncheck "Link Sun To View" and then do "render animation" as a sequence of frames. (BMP on PC, and PIC on Mac.)
I really recommend Bryce 4 to lots of people doing this kind of authoring work, because its heightfield exporter is absolutely unbelievable (if you remember to check the Adaptive LOD button). It'll make a great fractal heightfield, with adaptive LOD, specular, diffuse, bump textures, etc.
Oh yes, here's the file: cubemap.zip.