I've always been interested in the "British Arm" of the early days of British role-playing. Much like with the "US West Coast" style, they brought a different energy and style to that particularly Midwestern mode of fantasy role-playing and Dungeons & Dragons. The British, after all, are the ones who brought us The Fiend Folio and Warhammer Fantasy Roleplaying. Of course, they also brought us the Monstermark, so I guess that you take the bad with the good.
What makes this document so interesting is that it is a snapshot of an approach to fantasy RPGs that really doesn't exist any more. Some of it still exists in some forms in places like Warhammer Fantasy Roleplaying, but what you get in its current form is different from what you got as a game back then.
If I were starting a new game right now, I would probably dig into The Collected Pelinore as my setting. It is a realized world with interesting NPCs, maps, and some interesting rules variants for your old school D&D-ish fantasy games. One of the things that I found interesting was the section on capturing monsters (instead of killing them) for use in an arena, and how to calculate XP rewards for that. "The Arena doesn't want unfettered aerial monsters - who is going to pay to watch a harpie fly away?" That's just a great quote.
Ultimately the reason that I am spreading this around is because I think that we could use more diversity in our old school conversations. What people like Gygax and Arneson did to give us our hobby was a great thing, but getting to see the weird and wild directions that people take this hobby into is a great thing, too.
Update: Thanks to +Tim Huntley (in the comments), here is a link to a site that has scanned and compiled the original Pelinore into a PDF. I haven't read through this PDF yet, so I don't know how complete it is. The truth may lay somewhere in between this PDF and The Collected Pelinore. This is useful as much as an historical document, much like the Fiend Factory file below.
Update 2: +B. Scot Hoover, the architect of The Collected Pelinore is also archiving the Pelinore modules. Right now you can find two of them (In Search of the New Gods and The Awakening) on his Google drive. In Search of the New Gods is for characters 4-7th level, and The Awakening is for characters of 7-8th level. I'll leave this here for right now, but I will probably break these modules out into their own blog post once a few more of them come out.
A big thanks to +B. Scot Hoover for all of this hard work in preserving a piece of gaming history.
As an added bonus, I give you a compilation of the old Fiend Factory monster articles from the old days of White Dwarf. You may recognize many of these from when they ended up in the Fiend Folio, but these are the original versions of these monsters, as they were first published. Some are for D&D and some are for AD&D (the emphasis changed in the magazine when the new edition of the rules came out). This PDF is old and shop worn, and has been circulating the internet for a long, long time. I'm sure that most of you have seen it by now, but it is still a good artifact and for those few of you who haven't seen it...here it is.