Artist: Jim Holloway
Source: cover of I5 - Lost Tomb of Martek
Locale: The Skysea
Rationale: It's got a weird boat, a crystalline lake, a starfield, and a big purple shai-hulud wannabe. The image tickles the gonzo sea-faring itch, while the module trilogy is the one that launched my love of desert adventures.
* This topic was tough, too! Turns out there's plenty of "iconic" D&D imagery in my head, but little of it matches what's in the books. My memory is plagued by, umm, "embellishment."