SparkNotes is a website that offers study guides for a wide variety of topics, including "Animal Farm." CliffsNotes is a similar and equally useful study guide that has a summary.
In addition to the plot summary, SparkNotes also provides analysis, study questions and a sample quiz. CliffsNotes offers a detailed analysis and comments on Orwell's inspirations and intentions and the ideas Orwell presents in the book.
Many editions of "Animal Farm" also feature a low-level plot summary in the introduction, and further analysis can frequently be found in college and high school syllabuses that are provided online, although they are sometimes blocked from public access.