There are several sites that host information and resources for Game Masters to improve their game. I am unable to add all the sites out there but I will add sites that I find particularly useful or complete. Specialized sites may be added as well for diversity of information.
|Pathfinder SRD||The official d20 Pathfinder SRD site. This is pretty comprehensive with nice citations as to where things come from. This is mostly where I link to in regards to remote SRD material.|
|Dingle Games||A host of useful generators such as NPC, Monster, Treasure, and more. There is a subscription for advanced features but the free service contains some pretty useful stuff.|
|Archives of Nethys||One of the most complete Open Content collections outside of the official Pathfinder d20 SRD. As well as hosting a full SRD for Pathfinder 1st and 2nd Edition, there is also a selection of random generators that can be useful.|
|DriveThruRpg||A huge collection of PDF companion books covering a host of information. The sheer volume of available content is somewhat daunting but if you want to get some interesting additions to your game for a small investment this is a good place to start looking.|