Problem: It’s difficult to go through the musical examples. One must look for the recordings, or try to play them on an instrument (or sing). In some books, musical examples are printed in a separate section and referred through out the book (Refer: Ex. 1…). This makes reading the book unnecessarily complicated while the material discussed itself may not be that difficult.
Here are some fantastic resources, all Free!, both for listeners and music students.
For Listeners: to know better about music.
Sound Reasoning is a web-based, introductory music appreciation course. It offers a new approach to music appreciation for adults, focusing on style-independent concepts.
Short-and-sweet descriptions and lots of musical examples ranging from Gregorian chants to contemporary music. A typical page in the course looks like this.
Sound Reasoning, by Anthony Brandt
For Music Students
This site has excellent supplementary materials for Harmony and Analysis. The school suggests Aldwell-Schachter’s book on harmony. This site has examples – scores & and associated audio recordings, for the theoretical matters discussed in each chapter of the book, with some descriptions. The examples make sense even without the prescribed book.
Alan Belkin has written some very rich articles on Form, Harmony, Orchestration and Counterpoint. It’s very nice of him to share them all with us. These articles are online since early/mid 2000s. He says these articles are not meant to replace textbooks. True, but I’d suggest any student to go through the corresponding paper here before starting to read a book on harmony or orchestration.
More from Belkin: Principles of Orchestration Online, based on Rimsky-Korsakov’s book with the same title.
… and some more
http://imslp.org/wiki/Category:Music_theory – Music Theory books in Public Domain: (Including books on Harmony written by Schoenberg, Schenker, Tchaikovsky, Rameau; and on Orchestration by Berlioz, Forsyth, Rimsky, etc.)