There's a saying that the Golden Age of science fiction is 12 -- I suspect (and have said before) that Dragon works similarly, in that most people seem to think the best issues are the ones that came out around the time they first discovered the magazine.
With that said:
I second the recommendation for Paths of Magic. I never got to try it out, but it looks like a great way to add flavor to wizards.
There's a great series of articles by Tom Moldvay in #126, #138, #162, and #198 that goes through the literary and folkloric inspirations for a bunch of kinds of undead (and stats up some variations on the major themes).
Like Illithids? Issue #150 has "The Sunset World" -- a snippet of a setting ruled by mind flayers -- and the "Dragon's Bestiary" in which the Illithidae (3.5'ed up in
Lords of Madness) made their debut.
#170's "From Hatchling to Immortal Guardian" has an interesting take on the draconic life cycle. It was originally written for BECM D&D, but the ideas are eminently stealable.
Allen Varney's article
Turkey's Underground Cities is available online, but the illustrated version is in Dragon #201.
Also, you should know about the
DragonDex subject index. It's a very handy way to find Dragon articles on whatever you happen to be interested in at the moment.