I'm a big fan of art that explores unusual topologies:
Peggy Wyman
Rebecca McEntee
Peggy Wiedemann
Charles O Perry
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Carlo H. Séquin
I also like models of polyhedron and the like:
George W. Hart
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Bathsheba Grossman
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And hyperbolic planes:
Daina Taimina
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I'm amazed by these tessellations expressed through origami:
Eric Gjerde
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And the intersection between programming and origami:
Robert J Lang
See Also:
Mathematicians Get Crafty with Geometry
A Cabinet of Mathematical Curiosities
The Extreme Sport of Origami
Virtual Math Museum