I'm a big fan of art that explores unusual topologies:
Peggy Wyman
Rebecca McEntee
Peggy Wiedemann
Charles O Perry
Carlo H. Séquin
I also like models of polyhedron and the like:
George W. Hart
Bathsheba Grossman
And hyperbolic planes:
Daina Taimina
I'm amazed by these tessellations expressed through origami:
Eric Gjerde
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