Undergraduate philosophers at Cambridge take several courses in formal logic. As far as possible, I think it is best to teach these courses with open-access ebooks. We currently use the following:
The links will take you to a page describing the book, and allowing you to download it (in various formats). Both books are released under CreativeCommons ShareAlike licences. This means that they are available to download, share, and remix, free of charge (subject to minor constraints).
Last modified 31 Aug 2016