Google Book Search is a vast collection of digitized books, many of them downloadable for free, including many McGuffey readers, books about spelling, arithmetic, and classics such as Alice in Wonderland.
You’ll have to search creatively and very specifically, search by “full view” instead of “all books” or “limited preview and full view.” Even then you will have some results that are not downloadable, or not the full text.
Still, there are many books available that you can download and then read on the computer or print out to read. Considering the cost of McGuffey Reader sets, this site would be valuable if only for the point of printing the readers and assembling into a binder.
