Two years ago I blogged about my decision to use an older edition of my Contracts casebook instead of the newer edition. This saved my contracts students about $200 each which totaled about $10,000 for the class. The law of Contracts changes only glacially, and the students miss out on little by using an older edition. Although the cost of casebooks is only a fraction of the cost of tuition, the students appreciated the gesture that put some money back in their pockets.
This year I am doing the same thing with my Corporations class, although I'm not buying all the books myself as I did in my Contracts class. (The expense was minimal but keeping track of hundreds of pounds of books was a nuisance.) Corporations changes a bit faster than Contracts, especially to the extent one teaches securities regulation as a part of the class. Still 90%+ of the material hasn't changed since the 2010 edition date.
This practice does not work well for all subject areas. For example, I do not assign older editions in Securities Regulation class, which changes a bit too fast.
I hope other law school professors will follow this lead and assign older editions, especially for 1L classes such as Torts, Contracts, and Property. Such a practice adds little to the professor's workload (and may actually be easier as there is no need to update a syllabus for a new edition), and would save law students tens of millions of dollars in the aggregate. There are many ways to lighten a law student's financial load, if only we take a moment to put ourselves in their shoes from time to time.
POSTSCRIPT UPDATE: Several commenters on Facebook and Twitter have suggested developing one's own materials instead. Although that solution is right for some professors, it is not likely to appeal to a wide swathe of them as it takes a great deal of time. Unless one teaches a highly customized course, that time is likely redundant of the efforts already expended by others and could be better deployed elsewhere. Moreover, a commercial casebook already through several editions is likely to be higher quality than a new free one a professor puts together. Finally, many students will print out the "free" materials, costing them more than simply buying the old edition for $5-10. Thus, using the older editions is a better approach than developing one's own materials in most cases. Thanks to the commenters for these important points.