IMO, 2E was kind of a low point for adventures. Some good 1st edition adventures are the aforementioned Under Illefarn, and I really like Ravager of Time as well (although I haven't run or played it).
If you're willing to consider 3E material, I'd recommend Forge of Fury and Red Hand of Doom. I'm glueing those together to form a post LMoP campaign, although I have heavily modified my starting area to make it amenable to a RHoD invasion scenario. Forge will basically be repopulated and redone to be in the L5-8 range, and RHoD will be totally redone keeping only the basic ideas and plot lines. ie instead of the Ghost Lord, the invaders will have stolen Agatha's pseudo-phylactery and holding it in Leilon in order to force her to co-operate by supplying ghost treants for the northern offensive.
After I'd decided on those (based only on my appreciation of them as standalone adventures), I noticed all were written or co-written by Rich Baker. So I now consider him my favorite adventure author of all time.