Useful links:
A site on orchestration and instrumentation put up by the Indiana University School of Music. Very informative, with real players performing the instruments. Provides ranges, transpositions, and the like. The site may look like just a demo, but it’s fully functional.
An open-source (free) notation program, with traditional graphical user interface.
A free, command-line notation program. Excellent output, rivals Finale and Sibelius for quality.
A free online notation solution.