I'll weigh in here - for me, the Dragon of the late '70s and early '80s had a lot of excellent material in it.
And I especially enjoyed Dragon from about Issue 274 to 290. Why?
How to Create a Feat - includes examples, tips, "metagame thinking" and so on.
How to Create a Monster - ditto
How to Create a Prestige Class
How to Design a Weapon
How to Design a Spell...
Well, you get the idea. In other words, all of the "behind the curtain" stuff that really should have gone into the DMG in the first place.
Other stuff:
"Better Living Through Alchemy" - Expands on the uses of an existing skill. Also great for low-level campaigns before you want to give out magic items but still want to wow the PCs.
Dwarves, Halflings, Gnome, Half-Orcs, Elves - the "race issues" (pardon the pun) dealing with the default culture, language, viewpoints, and so forth. Not too useful for a vet like myself, but invaluable for "newbies" like some of the guys I gamed with.
The Ecology of the Darkmantle, Sheet Ghoul, etc. These give you the "why and how" a creature exists, not just the stats. As a DM, I appreciate knowing the monster's motivation.
The early prestige classes were nice when PrCs weren't so thick on the ground as examples, though now they are all but unneeded.
These days, Dragon lacks these "flesh out your world" articles and instead has "optional rules" to replace the ones in the core books. Not bad, I guess, but I don't want "optional rules." I don't want to replace rules I already have. I want to get new rules for areas where there aren't rules yet (bardic music is still woefully unexplored in WotC/Dragon).
I guess what I really want to see more articles that complement and expand on my existing stuff, rather than articles that are trying to replace it. Does that make sense? I don't need new gladiator rules or swashbuckling rules or other such silliness (new feats to emulate this are okay where no such mechanic exists - such as a Feat that lets you use a wall as a flanker for instance)... I already have the core rules which handle such things fine. I prefer Prestige Races. I prefer zombie/skeleton/mummy templates rather than basic creatures from the MM (to add flexibility - not the same as "replacing"). I want rules for weaponst that advance along with your character (all of the above have been done in Dragon and I liked that).
I REALLY want mass combat rules. I want underwater combat rules. I want rules for ruling a kingdom (a la the old Companion Set). I want rules for seige engines vs. structures. IOW, I want stuff that isn't covered under the existing system. Not an alt.gladiator or alt.swordfighter or what have you when I already have a fighter w/feats. I certainly don't want "more evil" and "yet more evil" and "still yet more evil" (see Dragon 300).
I want GENERIC, not WORLD-SPECIFIC material. I don't want more "economy of the Realms" - I do want "simulating economies." I don't want "NPCs of the Realms" - I want "how to run generic NPCs." I certainly don't want fiction. This is a fantasy GAMING magazine, not a fantasy FICTION magazine. There can be fiction but it should be *directly* tied to the gaming (e.g., "Ecology of..." is good but not "Bob's Adventures in Faerun").
--The Sigil