What's a good location to host a business conference in Cincinnati?

SuzM named several good ones. There's also the Sharonville Convention Center on Chester Rd in Sharonville just outside Cincinnati: http://sharonvilleconventioncenter.com/

It really depends on the size of conference you are planning, because there are a variety of venues around town to host one in. For larger conferences, you can use either the Duke Energy Convention Center or the Northern Kentucky Convention Center in Covington. There are also a number of hotels Downtown with large meeting spaces (such as the Westin). The Kingsgate Marriott Conference Center at the University of Cincinnati is a relatively new and nice facility for hosting conferences and events.