1) "Teaching English as a Foreign Language for Dummies" by Michelle Maxom, published by John Wiley and sons. Really easy to understand, and has everything that was in the weekend course, and more. It's very readable for just sitting in an armchair and reading from cover to cover. I also find it great as a reference book.
2) "Teaching Skills for Dummies" Again, really clear, and could help you avoid a lot of pitfalls in the classroom.
3) "Collins Easy Learning Grammar and Punctuation in Colour" Very easy to look something up quickly when you are stuck.
4) "English Vocabulary in Use", by Stuart Redman, published by Cambridge. I found this useful, again as a reference when planning lessons, to use for inspiration and guidance. It is really meant as a workbook, but I found it useful in other ways, too.