Jarian Gibson
Great website / blog with lots of up-to date information  and comments.

Virtualize my Desktop
This site strives to provide an understanding, through numerous means, of the practices and examples of desktop virtualization implementations.

DABCC
Doug Brown’s resources for everything and home of the DABCC Methodology in a Box.

Project Virtual Reality Check
Independent validation and research into desktop and application virtualization.

SimonBramfitt.com
This blog attempts to look for the key insights into the technologies and business ideas that will continue to influence application delivery and desktop vitalization in the enterprise

XenDesktop Design Handbook
The XenDesktop Design Handbook is the source for XenDesktop reference architectures, planning guides and best practices.

EdgeSight Under the Hood
The best EdgeSight resource on the Internet.

Zenapp.blogspot.com
About XenApp 5, XenApp 6, Presentation Server, or whatever Citrix call their products this week.

Thomas Koetzing
Best Web Interface site available

Jeff Muir
Jeff has been working for Citrix for some 16 years and is a member of the Citrix Labs team.  A great site from one of Citrix’s best.

Jason Conger
Jason is a MVP and CTP,  his site is full of articles based on his vast Server Based Computing experience.  Well worth some of your time.