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A guide for new DMs: Getting into fantasy D20
Dungeons and Dragons: Players Handbook: Vol 3.5Dungeons and Dragons: Players Handbook: Vol 3.5 by Monte Cook
Buy used from: £39.49
First things first- A players guide will tell you the basic rules and how to create characters
Dungeons & Dragons Dungeon Master's Guide: Core Rulebook 2, v.3.5Dungeons & Dragons Dungeon Master's Guide: Core Rulebook 2, v.3.5 by Monte Cook
Buy used from: £24.02
Once you know those basic rules, get this. The 3.5 version has vast amounts of inspiration.
Dungeons & Dragons: Monster Manual 3.5Dungeons & Dragons: Monster Manual 3.5 by Monte Cook
Buy used from: £34.49
Now you have your world and your dungeons...So populate them with denizens from here.
Dungeons and Dragons Roleplaying Game: Core Rulebooks (Dungeons & Dragons(r) Gift Set)Dungeons and Dragons Roleplaying Game: Core Rulebooks (Dungeons & Dragons(r) Gift Set) by Monte Cook
Buy used from: £214.55
Alternatively, of course, just pick up the above three titles together in this bundle.
Deluxe Dungeon Master's Screens (Dungeons & Dragons v3.5 Accessory)Deluxe Dungeon Master's Screens (Dungeons & Dragons v3.5 Accessory) by Wizards Of The Coast
Buy used from: £4.55
By no means essential, but a DM's screen will keep your schemes away from those players.
Forgotten Realms: Campaign Option (Dungeons & Dragons Accessory): Campaign SettingForgotten Realms: Campaign Option (Dungeons & Dragons Accessory): Campaign Setting by Ed Greenwood
Buy used from: £10.00
Got the basics, but can't be bothered to make a full world by yourself? Pick this up! Forgotten Realms is excellent!
Unearthed Arcana (Dungeons and Dragons v3.5 Supplement) ("Dungeons & Dragons")Unearthed Arcana (Dungeons and Dragons v3.5 Supplement) ("Dungeons & Dragons") by Andy Collins
Buy used from: £31.94
Not satisfied with the standard rules? Try this: Its a bundle of great alternate rules.
Draconomicon: The Book of Dragons (Dungeons and Dragons v3.5 Accessory)Draconomicon: The Book of Dragons (Dungeons and Dragons v3.5 Accessory) by Andy Collins
Buy used from: £18.50
Now the extras: Dragons have always been central to D+D, and this book goes into fascinating detail about them.
Book of Exalted Deeds (Dungeons and Dragons v3.5 Supplement) (Dungeons & Dragons)Book of Exalted Deeds (Dungeons and Dragons v3.5 Supplement) (Dungeons & Dragons) by James Wyatt
Buy used from: £17.84
What about encounters with celestial beings of good and angels? Get this.
Book of Vile Darkness (Dungeons and Dragons 3rd Edition Accessory)Book of Vile Darkness (Dungeons and Dragons 3rd Edition Accessory) by Monte Cook
Buy used from: £27.95
Or the opposite perhaps? Plunge your players into the depths of evil with this.
Epic Level Handbook (Dungeons & Dragons 3rd Edition)Epic Level Handbook (Dungeons & Dragons 3rd Edition) by Andy Collins
Buy used from: £15.00
You've been playing awhile and find you need greater challenges...so go epic!