This is probably fairly obvious but maybe not as obvious as it should be. If you would like to find online Citrix documentation, go to the Product Documentation Quick Links. Everything that is available looks to be here.
One of the most popular links would be Presentation Server 4.5 and Components. It looks like the documentation isn’t going to change to XenApp until Delaware ships.
The page with all the documents is updated regularly so it should reflect any recent additions.