What materials are considered "essential" for a new GM running a module?

[Sean D.]

Beyond the Core Rulebook, is there anything I would need as someone new to Pathfinder looking to run an introductory-level Pathfinder Society-sanctioned module for a group of online players?

[Grishnackh]

Sean D. wrote:

Beyond the Core Rulebook, is there anything I would need as someone new to Pathfinder looking to run an introductory-level Pathfinder Society-sanctioned module for a group of online players?

Some way of rolling dice (programm or a combination of dice + trust in the players)

Players would be good, too
And either a Chat program or voicechat

that would be the bare minimum ;)

[Dreaming Psion]

I'd probably go for the Bestiary I and maybe the Advanced Player's Guide (seems to be the most widely referenced book outside of B1 and the core rulebook.) Most of the other stuff referenced but not included you can find in the PRD for now: http://paizo.com/pathfinderRPG/prd/