At my job I'm involved with various research in low frequency radio
astronomy. Maps of the radio sky at frequencies of 10s to 100s of MHz are frequently needed and to satisfy these demands I created a C program called LFmap that can generate such maps in equatorial or galactic coordinates, in plain text or FITS formats. I wrote a techincal memo for the Long Wavelength Array project about it, available here.
A tar file with the LFmap source files is available: LFmap_1.0.tar.
LFmap is not unique, here's a link to the Global Sky Model, a most excellent map generating program.