I really like

Andrew Burgess
www.avalonart.com

Fine Arts College, Hampstead
www.hampsteadfinearts.com

Stephen Wiltshire
www.stephenwiltshire.co.uk

The Prince's Drawing School
www.princesdrawingschool.org

George Butler
www.georgebutler.org

Tommy Kane
www.tommykaneillustration.com

Karen Neale
www.karenneale.co.uk

School of Visual Arts
New York City
www.sva.edu

Danny Gregory
www.dannygregory.com