Wings 3D (
www.wings3d.com) has an excellent UV-mapping utility built into it. If you want to export to .X you'll need the development version (0.98.36) - the "stable" version has not been updated in ages due to some obscure problem with Mac OSX or something. There's also an "experimental" version (0.98.37-SE) which is not maintained by the official maintainer - you'll need that if you want to use GLSL-to-UVmap texture baking, since it got broken in 0.98.36.