Continuing a bit with the unplanned theme of the week my favorite resource during the 1E & even 2E era was Dragon Magazine. I have a copy of every Dragon Annual published to date. This includes the first one with the original ads from 1980 which I use as back-to-basics inspirational material when I feel a little lost running a campaign.
The second volume had a bunch of material from my original time with AD&D and Dragon
The third volume had Roger Moore's races and racial god articles among other things.
These first 3 volumes were much-used resources during my AD&D years in the 1980's. I was constantly going back and reading through them when starting or running campaigns or when trying to figure out a new angle for a new character. I would recommend them even today if someone was running a 1E campaign - they give a very good sense of the feel of the era. Love those cover prices too.
Volumes 4 &5 pretty much finish out the 1E/2E era for these things. I acquired these later so I was not as attached to them as the first 3.
There were several more traditional volumes during the 3E era but I was not terribly impressed with them, especially compared to the older volumes. However, once Paizo took over publication from WOTC they went and put together a very cool product called the Dragon Compendium which included 3E updates of things from all through Dragon's history. This include 1E material like the Death Master class. It was definitely a grab-bag approach but there was some good material in there. Plus it was a nice, big full-color hardback - that doesn't hurt. There was hope that there would be additional volumes, but that never happened.
With the launch of 4th Editioon D&D in June of 2008 WOTC adopted a new policy. Dragon would now be on-line-only, ending the 30+ years of the paper magazine's run. This did nothing to convince me that 4th was a good idea and in fact was a mark against it in my eyes as it was behind a paywall. I ignored it, much as I ignored 4E at the time. Fast-forward to 2009 and my interest in 4E begins to come back around after a year or so of ignoring it. In August of 2009 WOTC published the Dragon Magazine Annual, billed as a collection of the best material from the 1st year of the 4E online dragon. I read some reviews not long after it came out and was unimpressed - the reviews had a lot of "I already have this online" and "this is pointless" type comments and the material discussed didn't seem all that impressive or useful.
Fast forward again to August of 2010 and I am actually running a 4E campaign and have been furiously playing catch-up on 4E books. I came across a very reasonably priced copy of this book online and decided to pick it up for completeness sake. It's a nice 160 page full-color hardback and having read through it now I have to say this is actually a very useful book - details below.
DM Material: The book opens with an article on Yeenoghu, demon lord of Gnolls and reading it after having read Manual of the Planes it fits extremely well into that material - stats, new monsters, descriptionos of Yeenoghu's home plane, and a sample secret cult of his followers.
Next up is an article on Kobolds that includes 8 new kobolds and some suggestions on traps they might use in their lairs. It's only a few pages but it's immediately useful in a low-level campaign as kobolds show up regularly in levels 1-5 especially. It just so happens that the area of my campaign that my players are getting to happens to be infested with kobolds - and yes they were revised a bit after I read this article.
The Ashen Covenant is an article on cults of Orcus, specifically one that is not just about random destruction and sacrificing of maidens, but one that has a larger goal and several plans on how to get there. It includes adventure hooks, NPC stats for the cult leaders, and some new monsters & magic items. I like this kind of thing because even though Orcus is not set to play a big role in the campaign right now, knowing I have an article like this gives me a pre-made cult to drop in if a player takes an interest in fighting Orcus or picks some kind of paragon path or epic destiny involving him. Basically something could come up in one session and knowing that I have this I could lay some groundwork and then make it a set part of the campaign by next session.
Mithrendain, Citadel of the Feywild is a location description of an Eladrin city in the Feywild. It reads like an entry from Manual of the Planes. It includes a description, NPC stats for notables and guards, some new powers and feats for players associated with the city, a paragon path, and some new magic items. Again we have a nice drop-in location that gives me a specific place in the Feywild if I need one on short notice for the campaign. If I have a player who wants to be from the Feywild, I have a nice little article to give them. If the party ends up spending time in the city then i have some specific goodies to give them related to it- this is exactly the kind of material that 4E needs more of - useful nuggets.
Later we have the Bloodghost Syndicate, a secret criminal organization run by bugbears. This didn't tickle my fancy as much as some of the others but it's a nice descriptive article that includes some NPC's, some new monster types, and a sample hideout. Again it's a nice drop-in organization with a short history and some defined goals that's not tied to any particular campaign world so if the need arises I have another badguy group I can play if I need one.
Intelligent items is a short article on adding intelligent magic items into your 4e game. This is a callback to older editions of the game and I like to see this kind of thing showing up in the current edition. It's mostly a discussion of how to implement them and it contrasts them with artifacts which have already been described in the game as being intelligent. It's a good article and has a lot of examples and sample items to illustrate the techniques and approach described.
There is a short adventure description about a red dragon. It's a level 11 encounter with some setup that is kind of a reverse-Christmas scenario. It's only a few pages but it is again a nice drop-in thing that could help out if the players are traveling or to set up a future fight at low levels.
The biggest section of the book is a 30-page section (divided into 2 articles) on arena fighting and gladiators. I have to say this was the section of the book I enjoyed the least. It's a good article and all but this is not something that has ever come up in my D&D games in the past (I did run some arena fights in a Rifts campaign but that's the only time) and I don't expect it to come up in a campaign anytime soon. Plus, this isn't the kind of thing I would just drop in to a game either - it takes some setup and planning to integrate into an ongoing campaign and it's not part of the classic dungeon romp so it seems to me to be a bit of a limited subject for such a big chunk of the book. I also suspect that it's been superseded by material for the Dark Sun campaign, making it even less useful now. Maybe not, but outside of Dark Sun I can't see it coming up regularly. I don't dislike the material, it's just of more limited usefulness than a lot of the rest of the book.
The book wraps up with 4 articles that are mainly player-focused.
Playing Dhampyr is of consuming interest if you have a player that wants to play a vampire PC right from the start. I haven't tried it but it looks well done and gives background, feats, powers, paragon paths, and a few new monsters. With all the attention on vampires ala Twilight and True Blood I can see this one getting some use in an otherwise typical campaign.
The next article is Masters of the Planes which is a set of epic-destinies related to the various outer planes. I thought the Prince of Hell was pretty interesting as it's somewhat similar to the ascension of a chaos lord in Warhammer.
Playing Shadar-Kai is the next article and it's as complete as the Dhampyr article, so if you have a player that wants to play something pretty exotic then this should work. They don't strike the same chord with me as the vampire article did but I can see them having a place in some campaigns.
The final article is Art of the Kill, a discussion of assassins and assassination that includes backgrounds, feats, paragon paths, and items related to these things. I can see it being somewhat useful but my players aren't really inclined in that direction so it will probably not see much use in my games. It does look like a pretty thorough handling of the non-shadow powered assassin in 4E.
So what do I think overall? I think it's a damned handy resource for the 4E DM. I thin kit's a waste of money for a player as most of the content is aimed at DMs. Those first six articles make the book for me as I can see ways that all of them could come up in a game in general and in my game specifically over the next few months. I can't really give it any higher praise than that. I will say however that the $29.95 cover price is high for this book. Compared to something more focused and mechanically useful like the power books this is a grab bag product that will likely be used in limited chunks over several years. Look for it on sale or online or in some discounted form and I expect you will be happier with your purchase.