Sometimes it is just more comfortable reading source code on paper, but printing directly from a text editor often gives an output that is ugly and wasteful. Just try opening up your source code in notepad, textmate, etc. and print. It might look very nice on your screen but on paper the fonts are big with lots of white space.
Printing source code is a different beast then printing narrative text and has some special requirements. The first is to include line numbers for easier reference. Different languages have different formatting and sometimes you want to print with color syntax to help find what you're looking for. It can also be helpful to print two pages on one sheet so you can see more of the code and reduce paper waste.
On Windows/DOS, programmer editors usually have features for handling these types of pretty source code printing. Strangely, none of the editors I've seen on OSX have it (TextMate, Eclipse, Smultron, etc.) and since I've been dealing with code more I wanted a solution.
Fortunately, OSX's UNIX underpinning allows me to use the classic enscript tool to handle this.
enscript -2 -q -C -Ec --color -f Courier8 -r -p OUTPUTFILE SOURCEFILE
This generates a Postscript file (default), with 2 columns (2), quiet mode (-q), line numbers (-C) , using C syntax (-Ec), in color with Courier 8 pt font (-f), in landscape mode (-r) to a file called OUTPUTFILE (-p) from SOURCEFILE.
You can find different language syntax available for the -E option with "enscript --help-highlight" and you can set different output formats besides PostScript with the -W option (i.e. html).
"-p -" will tell enscript to print to stdout so you can pipe it to lpr.