Because we're in the habit of making lists in this forum I'm feeling a strong compulsion to make another one... this time the theme is "orchestration and composition":
Understanding Basic Music Theory
An expanded version of "Introduction to Music Theory", this course includes a review of common notation and an introduction to the physics behind music theory, as well as the basic concepts of music theory and a few slightly advanced but very useful topics, such as transposition. (CC-BY licensed)
Theory on the Web
Excellent introduction to tonal harmony and part writing that the music from the common practice era (i.e. "classical music") is built upon.
Tonal Harmony by Stefan Kostka
The leading text book about music theory and tonal harmony. A must have in your library!
Composing Music: A New Approach by William Russo et al.
A book aimed at those who have some knowledge of music but not formal training in composition, this concise introduction to composing starts right in with a brief composition exercise, then proceeds step by step through a series of increasingly complex and challenging problems. Another must have in your library!
Principles of Orchestration On-line
Open To All without Charge! "Principles of Orchestration", based on Rimsky-Korsakov's classic text is now online. In this interactive edition you will be able to simultaneously hear and see examples where audio follows the score. These courses are offered free of charge at the Northern Sounds forum.
The Technique of Orchestration by Kent Kennan
The emphasis is on the practical fundamentals of orchestration and widely used as a classroom text. A good reference and a good complement to "Principles of Orchestration On-line" (see above).
Instruments Online, created by Vienna Symphonic Library, is a unique free multimedia instrumentology which includes the essentials of instrumentation. A good source for ideas about what instruments blend well together. Aside from the usual orchestral instruments it will introduce numerous rare instruments, so Instruments Online will continue to grow and grow.
Acoustic And Midi Orchestration For The Contemporary Composer by Andrea Pejrolo and Richard DeRosa
Complete guidance on both traditional orchestration and modern production techniques. With effective explanations and clear illustrations, you will learn how to integrate the traditional approach to orchestration with the modern sequencing techniques and tools available. You will discover how to bridge the two approaches in order to enhance your final production.
Twentieth Century Harmony: Creative Aspects and Practice by Vincent Persichetti
An orderly presentation of the harmonic procedures to be found in music of the first half of the twentieth-century. The author examines the nature of intervals in various contexts, discusses the modes and other scales employed in modern music, describes the formation and uses of chords by thirds, by fourths, and by seconds, of added-note chords and polychords; and different types of harmonic motion, with harmonic rhythm and dynamic sand ornamentation, with harmonic behavior in tonality, polytonality, atonality and serial composition.
Jazz Arranging Online - by Prof. Chuck Israels
Interactive Edition of "EXPLORING JAZZ ARRANGING", based upon Chuck Israels' new book. Chuck Israels is a true jazz master and there simply is no better source from whom to learn about jazz arranging. These courses are offered free of charge at the Northern Sounds forum.
A blog post by yours truly. Despite its attempt at explaining jazz the article covers a lot of basic harmony applicable to all western music.
The Mutopia Project
The Mutopia Project offers sheet music editions of classical music for free download. These are based on editions in the public domain, and include works by Bach, Beethoven, Chopin, Handel, Mozart, and many others. A team of volunteers are involved in typesetting the music by computer using the LilyPond software.
More will follow later. TTFN!