Thanks everyone, I kinda cheated, combining a few similar books into one selection, and adjusted the categories a bit, but this is the text of what I wrote for the store (it isn't submitted yet, so feel free to convince me of something else):
Top 5 lists for Pathfinder Player Companions
This article deals with a question I’ve heard around the shop recently. “What other books should I look into getting?” Once you have the hardcovers, this gets to be interesting question, as there are many ways to prioritize what you want, So I’m going to give a number of my opinions on top 5 lists, based on what I enjoyed, what I have seen being used in games around the state, and what people are excited over:
Top 5 General Companions
*Pathfinder Society Primer - know who you're working for. The history of the society is a great thing for PFS.
***Champions of Purity/Balance/Corruption - these three books take one spot, because they are all equally useful, and fill the same role. Want to know how someone who worships your god acts? Look in the proper champions book
***Faiths of Purity/Balance/Corruption - similar to the above, but a bit more general information, not as focused on the divine casters
****Undead/Dragon/Giant/Demon Slayer’s handbook - these 4 books are packed with tips and tricks to fight the type of monster in the title. is you campaign set in the Worldwound, where demons rule the land? You might want to learn how to fight them then. Are you raiding a dragon’s lair? We have that too. Going to vanquish some sewers of a few variety of zombies and skeletons? Might want to know the difference first.
*Dungeoneer's handbook - Great tips for any beginner or intermediate player
*Honorable mention: The Strategy Guide - since its a hardcover, it couldn’t make the list, but even the most hardened game masters have said they learned things while reading the strategy guide.
Top 5 Martial Class Companions
You may see a pattern here. Melee classes are often defined by either their feats of their gear, so the crunchier ‘toolbox’ style books fit them well:
*Melee Tactics toolbox - lots of fun options for a wide variety of melee types
*Weapon Master Toolbox - I’ve heard talk that this book ‘actually fixes the fighter and puts him on par with a wizard at high levels’
*Dirty Tactics Toolbox - great for sneaky types, but there’s a little here for everyone
*Ranged Tactics toolbox - You want to be Green Arrow? Here’s some of your trick arrows, and feats to help you shoot .
*Advanced Class Origins - Some great options for all of the Advanced Class guide classes, but especially the Swashbuckler and Skald.
*honorable mention: Heroes of the Streets. I haven’t read this one yet, but it is the companion that currently has the highest review on paizo’s site.
Top 5 Arcane Spellcaster Companions
There’s a lot of ground to cover here, and there are not as many companions that deal with new spells, most of those require a campaign setting book. So these are a little all over the place
*Arcane Anthology - this one just came out, so I haven't read it yet, but the description is juicy for arcane content
*Monster Summoner's Handbook
*Harrow Handbook - Great essays about how to use a harrow deck (which you can actually buy BTW) in your games, both as a GM and a Player.
*Alchemy Manual - alchemists and investigators are the ones to get the most use out of this, but there are some alchemical things that everyone might like in it.
Top 5 fluff (story) player companions
*Pirates of the inner sea - because who doesn’t like pirates
*Black Markets - What do ye want? Shiver? Flayleaf? Pesh? Poison? We gots it here!
*Faiths and Philosophies
*Quests and Campaigns
*Magical Marketplaces - A listing of some interesting marketplaces around Golarion along with sample item lists.
Top 5 race/location player companions
*Blood of Fiends/Blood of Angels - If you’re building a Tiefling or Aasimar, you need these books
*Blood of elementals - the elemental races and notes on playing one.
*Bastards of Golarion - Ever want to play a half-elf or half-orc?
*People of the Sands - All about Osirion and Qadira the Egypt and Arabian Nights analogs.
*Varisa, Birthplace of Legends - lots of fluff, but Varisa has a lot written about it to sum up in 32 pages. Great for character ideas
Top 5 “must get” for one or two items
In PFS, everything you own you must have a legal source, either the book, or the watermarked PDF. These are the player companions that are ‘must haves’ for a single powerful feat/weapon/spell
*Sargava, the Lost Colony - This is the only source of the feat Piranha Strike.
*Animal Archive - The ‘flank’ pet command is only outlined here.
*Champions of Purity - a must have for Paladins. Know what your god expects of you.
*Blood of the Moon/Night - Have you ever wanted to play vampire or werewolves? That's basically what these books are about (not much is PFS legal in these, but great for home games)
*Elves of Golarion - There are some arrows here that were only printed here. Some were reprinted in Ultimate equipment, but not all.