Let's say I have two business service components which contain my BL controller classes (they are also located in diff. assemblies). One is Accounting and one is Sales. Now, accounting needs to use the services from the sales components, so the accounting dll has a ref to the sales component. Also, the sales has to use the services of the accounting dll, so he has a ref to the accounting dll. Since this is a circular dependecy, is this considered bad design?

I don't know if it's a bad design, but as I see it, your only other option would be to create a THIRD project that references your other two projects and use it for functions that require your original components.