I don't know of any tools that allow you to directly convert complex shaders from Maya or 3Ds Max to GLSL/HLSL (although if you do find it, let me/us know!). For simple shaders (lambert, phong) you can probably write your own parser (tools like Havok Content Tools already parse the shaders [again, simple shaders] and can give you a material which you can then use to create a GLSL shader in your program).
Maya's and Renderman's shaders rely on a complete framework with a lot of nodes. Moreover, they are designed to work with rendering engines that raytrace into the scene; so a shader can have many passes and many texture units and effects which can be impossible to translate to a single GLSL shader.
However, the opposite exists. That is, you can have your shaders work in the 3D packages which is one way to streamline your pipeline. For example, 3Ds Max supports MetaSL which in turn can be converted to HLSL/GLSL shaders. Maya supports rendering HLSL/GLSL shaders via a plugin which exposes supported attributes of the shader. Same with VRay. So instead of relying on their respective shader networks, you may want to create shaders in GLSL in the respective 3D programs which then makes it easy to export the shader as it is already in GLSL.