In this, probably last post (gotta keep my own wallet safe), I list my recommendations for materials compatible with TSR and OSR games. Most of the books bellow are settings and procedures, which makes it easy to take out elements you find interesting and use them in your game.
Dave Hargrave was a mad man. A very creative mad man. You might never play Arduin as written, which just like Palladium Fantasy was a bunch of AD&D 1E house rules, but you will walk away inspired like never before.
Arduin Trilogy. Compiles Arduin Grimoire Vol 1, 2, and 3. I still use special ability charts presented herein.
Arduin II. A first attempt to make a functional, stand-alone game after TSR and Gary turned on anyone who dared hack it.
Autarch is the publisher of Adventurer Conqueror King System, marvellous system built on B/X chassis. It offers superior take on domain management, race-as-class, functional and tightly integrated economy, and plethora of play-tested options for ambitious Judges and adventurous Players.
All adventures, except Dwimmermount, are set in Auran Empire, which is an ACKS setting. I've found all the adventures superb and easy to adjust (and steal from). AX3 has some great tables for urban dwellings.
It's that time of the year again. May our wallets survive.
After recommending some Troll Lord Games products on sales, it is time for Frog God Games.
My favourite recommendations are in fact re-issues of Necromancer Games material, a predecessor to Frog God Games, like The Lost City of Barakus,The Tomb of Abysthor, and Bard's Gate. And make sure to grab the bestiaries if you haven't already.
Great majority of the recommendations below are for Swords & Wizardry system, a retroclone of Original D&D. All statblocks have descending and ascending AC, and everybody uses a single save throw (but since HDs and levels are nearly identical, you can use TSR-era saves without any hassle).
MCMLXXV. Old-school wilderness treasure hunt. For first level parties.
Grimmsgate. A village, surrounding area, and dungeon suitable for first level parties. Dungeon is well made, with multiple entrances and uncommon foes.
Stoneheart Valley (Swords and Wizardry). A collection of three old Necromancer Games adventures: The Wizard's Amulet, The Crucible of Freya, and The Tomb of Abysthor. First one is shit, second is fine, and third is awesome.
The Lost City of Barakus (Swords and Wizardry) (local and regional maps). Perhaps my favourite Necromancer Games mega-dungeon—because it is so much more! You get a starting city (with seven adventures), a wilderness area (with 26 keyed encounters and mini adventures), and a mega-dungeon with interesting factions and cool big-bad. Suitable for low-level parties.
Cyclopean Deeps (Swords and Wizardry) (volume one and two). Underground hex-crawl for high-level parties. Includes underground settlements as well. Perfect for plugging into lowest levels of large dungeons... Or under sprawling cities...
Bard's Gate (Swords and Wizardry) (player's guide). A massive city packed with urban encounters and adventures (8 included, from levels 1 to 10+). Very dense book. Some say this is FGG's finest product. The truths is: this is another Necromancer Games revival. And that's why it's great. :)
Monstrosities (Swords and Wizardry). Nearly 500 monsters. Each monster comes with an example encounter/nano-adventure. Includes tables with monsters by challenge level, guidance on creating new monsters, tables of monsters by terrain, and tables of random encounters (3d6, so bell curve).
The Book of Taverns (volumes one, two, and three). Had enough of generic taverns and inns, but short on prep time? Steal one from here. Again, these are revivals of old Necromancer Games books. They are good.
Lost City of Gaxmoor (digital and isometric maps). A city that was gone for a thousand years reappears. Of course it's full of shit that wants to kill nosy adventurers. Plane of chaos breach the reality from time to time.