For the most part, the texts I require and recommend for my courses do not change from semester to semester. The main exception would be for new editions of the books. Thus, the best indicator of the books that will be needed for one of my courses is the past syllabus for that course. The current or most recent syllabus for a course is posted on that course's webpage (links at left) and the syllabus will indicate the author, title, and edition of the books ordered.
Despite the labels "required" and "recommended," how much any particular book is needed for a course depends on the book and the course. In other words, one may be able to substitute for some "required" books (e.g., the law dictionary I order for most of my courses) and some "recommended" books may be required (e.g., a book that may be needed for the paper topic chosen for 30:153). I talk about this at length during the first class period of the particular course.
New editions of books are usually more expensive and used copies may not be as readily available. Thus, students will sometimes ask if older editions of the books are acceptable. The short answer is that sometimes they are and sometimes they aren't. Again, it depends on the book and how it will be used in the course. This is something I discuss the first class period, but there may also be information regarding older editions on the syllabus or the course webpage.
I order all my required and recommended books through Iowa Book and Supply. In addition, I request that all such books be placed on reserve at main library.
In addition to required and recommended books, I also require coursepacks for most of my courses. These are available from Zephyr Copies. The cost varies, but is usually about $20 or less.