I incorporate business writing into most of my courses. I'm fortunate in that I had a business background before going into teaching. Also, many of the courses I delivered for IT involved business correspondence.
The main areas are letter writing (the four main type of business letter - requesting, acknowledging, complaining and confirming).
Business Englishis very formal with standard phrases which are far easier for students to learn (you can literally build business letters from stock phrases a bit like Lego).
Other areas include recruitment - job description, job advert (narrative style), CV (resume), covering letter, invitation to interview, letter of appointment/rejection.
Making, changing and confirming arrangements is another and you could try some report writing with them (but try to keep the reports short, maybe two pages).
Hope that helps a little.