Many thanks for this plethora of suggestions, I'll have my hands full tracking this material down
Some comments thus far:
1) I have looked at the later Freeport stuff (Black Sails over Freeport, Hell in Freeport). It looked really interesting, but the setting will need to be tweaked (IMHO) to fit in with my normal campaign (Realms based).
2) As for some of the older classic modules, I agree entirely. However, all of my players are quite familiar with them. I have only the fondest memories of the Saltmarsh series and some of the UKx modules. As a recommendation of my own in this context, I could mention UK6 All that Glitters (small, but very interesting dungeon content, mainly outdoors) and UK1 Beyond the Crystal Cave (technically a dungeon, but mainly investigative/social interaction). Thanks for the pointers to L1/L2, I actually have those, but had completely forgotten about them ...
3) As for RttToEE, my impression is that it doesn't quite fit my current focus of `non-dungeon' setting ;-). A couple of years back, my group aborted playing the original ToE after a couple of sessions since neither the players nor the characters saw any point in venturing further into the depths (which we found neither logical nor interesting). But as usual, tastes differ. This doesn't mean we hate all dungeons, to the contrary: I heartily recommend I3-5, the Desert of Desolation Series. It consists mainly of smaller dungeon-like sites set in very intriguing environs (Arabian nights-like).
If there is some interest, I can check my entire collection and comment on the best non-dungeon modules I have played thus far.
Again, many thanks for the discussion.