Many may think Citrix is more about Client and Desktop Virtualization, but Citrix is also one of the leading player on Application Delivery Controller business.
App Delivery Controllers are one of the key piece for successful Desktop and Server virtualization deployment.

Citrix is closing the gap with F5, and leaving Cisco behind. (source: Gartner)

2009
http://www.gartner.com/technology/media-products/reprints/f5networks/vol6/article1/article1.html

2008
http://mediaproducts.gartner.com/reprints/f5networks/vol4/article1/article1.html