For adult beginners and intermediate level students, I use Interchange by Jack C. Richards, published by Cambridge. This course starts with the very basics of grammar and vocabulary and steadily builds. It covers all aspects of language—grammar, vocabulary, reading, writing, listening and speaking.
At university, I use Inside Out, various authors, published by MacMillan. This course is a lot more challenging than the Interchange course, it has significantly harder reading exercises and more challenging grammar and vocabulary. Like Interchange, Inside Out is a complete course covering all aspects of language acquisition.