Language Reference for Business Enh
Brieger/Comfort

Basic English Usage
Swan, Michael

Vocabulary in Use
McCarthy, Michael u.a.

Him and Her
Schmidt/Wullen

Role Play
Ladousse, Gillian Porter

Situational Grammar Practice

How English Works
Swan, Michael;Walter, Catherine

Wirtschaftsenglisch
Baddock, Barry

Visual Dictionary
Merriam-Webster's

The American Heritage Dictionary