The crystallographic model-building and display program MIFit can read mmCIF diffraction data directly and compute the map internally i.e. you don't need any other software. There is a tutorial (lesson 16) on this exact application.
MIFit runs on Windows and Linux and is free to academics users. There is an installer for Windows and gzipped tar file for Linux http://mi.active-sight.com/download.html There is a lot of flexibility in rendering and image export. Thanks John Badger, Director of Structural Biology, ActiveSight
