My favourite textbook is the
World Link series published by Heinle. I used it with my uni students.
I really enjoy teaching it because all the activities are useful AND fun. Every page has pair or group work activities that actually start natural conversations about interesting subjects.
On top of the fact that the student and work books are good for the students, I like the teacher's book. It's well organized, the pages of the TB have the same page numbers as the corresponding SB pages (that's a small thing, but saves so much time and shows whoever put it together was thinking of the teacher), and there is so much extra material/ activity ideas and useful culture notes that the student's enjoy hearing about.
It's starting to sound like I work for them, but there's one more thing I like. Their student website has on-line dictations that the students can email directly to me, and other interactive activities to help them study vocabulary, etc. I swear I'm not being paid to rave on about them, I just really, really enjoy teaching this book.