I use "Interchange" or "Person to Person" for those false beginner classes even if they are in a company. They need to improve their English before they can take the jump to business English.
Many of the students and companies don't understand it. Use lots of pair work activities or group activities and expect one or two in the group to shine above the rest.
With the advanced students I would suggest "Business Basics" by Oxford. It's really good and should fit nicely for their level. Also there are tapes with it too if you want to use them in class. The book has a very business feel on it and it has lots of activites like emails, phone conversations, profile about different companies etc.
If you have any more questions then feel free to ask me!