Every Citrix administrator should know these pages:

Citrix eDocs – http://support.citrix.com/proddocs/topic/infocenter/ic-how-to-use.html
Manuals for all Citrix products.

Citrix KB (Knowledge Center) – http://support.citrix.com/
On that site you can find information about Hotfixes and Updates. You can also subscribe for some informations about interesing products there.

Citrix Discussions – http://discussions.citrix.com/
Discussion board

Citrix Community – https://www.citrix.com/community.html

Citrix Blogs – http://blogs.citrix.com/