Financial Accounting Developed by MIT Open Courseware. It requires that the user purchase the textbook for the class. Can still access course materials for free.
Principles of Accounting A comprehensive, online textbook with problems, worksheets, and quizzes, written by Professor Larry Walther, Head of the School of Accountancy at Utah State University.
Principles of Financial Accounting Course website for a Financial Accounting course at University of Alaska Anchorage with a textbook, presentation slides, quizzes, and exams.
Accounting Coach Website contains explanations of major topics, Q&A, quizzes, puzzles, etc.