Gartner publishes an examiniation of vendors whose products provide features that address the needs of systematic A2A, B2B and cloud-based application integration projects.

Microsoft, with its BizTalk Server product, comes out as one of the leaders in the Integration space.

Gartners published research: http://www.gartner.com/technology/media-products/reprints/microsoft/vol2/article3/article3.html

Source: http://blogs.msdn.com/b/nikosan/archive/2011/01/18/implementing-your-next-generation-integration-platform-from-gartner.aspx