I always thought that this Bohemian or Czech chess set had some Art Nouveau vibes, in particular the knight, but I may be mistaken.
And then this figural set, made in Erbach / Germany probably around 1900-1920, is very Art Nouveau in my opinion. Also the board, actually, which is not original to the set, however.
Stylistically somewhat different, but still from the Art Nouveau era, is this set made by WMF. It appears in the 1903 catalogue, but was probably made already since the late 1890s.
I always thought that this Bohemian or Czech chess set had some Art Nouveau vibes, in particular the knight, but I may be mistaken.
And then this figural set, made in Erbach / Germany probably around 1900-1920, is very Art Nouveau in my opinion. Also the board, actually, which is not original to the set, however.
Stylistically somewhat different, but still from the Art Nouveau era, is this set made by WMF. It appears in the 1903 catalogue, but was probably made already since the late 1890s.
Beautiful sets! The knight of the first set definitely looks Art Nouveau to me. What a cool design! I just realized I came across the black pieces from that very set last week when searching for original Česká Klubovka sets. Do you happen to know of any reproductions with such a knight design? Have you come across any similar sets at all, or is this one quite unique?
Neat to see doors and windows on those rooks in the third set! I only recall seeing that in the Best Chessmen Ever. Although I imagine some pre-Staunton rooks would have had such details as well.
But , then it would be like a kid in the candy store ! I want that one ,then that one , then this one , You would not be able to help yourself ? 
But you right class never goes out of style / just goes up in price .
Yes, quite Art Nouveau! Although perhaps leaning Art Deco. A really nice set, in any case. I happened to come across it again yesterday (having seen it before on chess-museum.com) and read about a plastic version of the set being sold as Gaudí chess pieces.
Here is a beautiful Joc Catalan reproduction by Chessbazaar (not the most faithful reproduction based on the sets I see on chess-museum.com, but entirely in the same spirit):
I came across plenty of chess sets that could be classified as Art Deco, but I haven’t really seen any sets that are distinctly Art Nouveau. Do you know of any?
The manes of the Westminster knight below do remind me of the Art Nouveau style, but I wouldn’t say the set in general evokes that style.
And since there are 800 Art Nouveau buildings in Riga—the hometown of Mikhail Tal—I figured someone might have capitalized on that association.
But while I see chess sets evoking Art Deco, Bauhaus, and even Dada, Art Nouveau chess sets seem to be curiously absent. Or am I just not recognizing the style in chess sets?