Besides the stuff in this thread, I'd also like to give a shoutout to the work of my favorite TSF tileset artist, (Drop)Mat:

• Shrunken Jazz has been used from time to time, but it's still worth checking out for how different it is from practically any other tileset. It's quite a substantial set, despite only using the sprite colors, and it's full of original ideas and inventive tiles. Levels using it all tend to look pretty much the same, and much like Chateau it has a pretty underdeveloped outside, but it's still a great set.
• MatBoard is obscure enough that EvilMike once championed it on his JJ2 blog as a totally unknown set, although he was talking about a presumably-earlier version with twenty fewer tiles and a different name. It's based on chess, dice, and playing cards, with some random pools and things thrown in as well. Like Shrunken Jazz, it's one of the most original sets you'll find, with great execution to boot. I imagine it predates Tomb Rabbit 2's chess-themed tileset, but TR2 was developed over so long a period of time, who knows?
• Subsurfacia is the most ordinary of the three sets, being set in an underwater temple environment with keys and gray blocks and such, but it's still really well done. Despite using the same small palette and simple shading as the first two, it's probably the best underwater tileset there is. It could, admittedly, use a bit more color and a few of the radical block ideas from Shrunken Jazz, but if you don't compare to its less orthodox brethren, it's a very usable set.

(Mat also made Neon City, but it's only worth downloading as a novelty or for the sake of completion. Like the others, it shows him making great use of an idea, but the idea itself -- a tileset made up almost entirely of corporate logos -- is so limiting that even Mat's creativity couldn't really make the end result worthwhile.)