Sites that have really done their homework and figured things out about the wonderful world of Tyria.

Dulfy.net: Dulfy puts out awesome articles and guides for all of the content around Guild Wars 2.  Here are the ones I find myself referencing all the time:

World Bosses: http://gw2.limitlessfx.com/ Tracks which boss is coming up and you can use it to track which ones you have finished for the day.

Ever wonder where to find specific resources? https://gw2efficiency.com/gathering/permanent-nodes Shows where all the farms and permanent nodes reside.