Better English

http://www.better-english.com/exerciselist.html

All the business grammar and vocabulary topics you could wish for!  There aren't really any lessons here; each page is just a quiz in a business context, but I find it a great supplement for grammar or special vocabulary.

 

Marcus Evans Linguarama

http://www.linguarama.com/ps/index.htm

This is a business site which has thematically organized exercises for reading, writing, pronunciation, style, vocabulary and usage.  

 

Talk English

http://www.talkenglish.com/Speaking/listBusiness.aspx

This has a fairly limited amount of topics, broken into several subcategories.  Each has conversation with listening. No exercises.