Mine are as follows:
Alex Gray http://alexgrey.com/art/
Andy Goldsworthy http://visualmelt.com/Andy-Goldsworthy
Roy Lichtenstein http://lichtensteinfoundation.org/
Alex Tremulis http://www.gyronautx...x-tremulis.html (He's an industrial designer so that might not count)
Ron Mueck http://www.boredpand...s-by-ron-mueck/
H.R. Giger http://www.hrgiger.com/
I'm sure my list will continue to grow if anyone can list other good ones who I may have overlooked or hadn't heard of.