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.