BooksHerstein's Topics in Algebra is another book that is at a roughly appropriate level for this course. It has a lot more examples than Isaacs, which I like. On the negative side, it is more verbose (sometimes overly so), and doesn't cover the important topic of group actions.
Another comprehensive algebra book at the advanced undergrad/beginning grad level is Dummit and Foote's Abstract Algebra. This book has a lot of topics in it (including a few not covered in Isaacs), and can be a good reference.
Anti-recommended: Herstein has another book called Abstract Algebra which is at a lower level, and probably a little low-level for this course. The algebra textbooks by Fraleigh and by Gallian are probably also a little low-level for this course.
WebsitesWikipedia is, perhaps surprisingly, not a bad source for background material on basic definitions and results in many areas of mathematics, including group theory.