JakPumpkin
Offering a variety of metal, including favorite licensed characters as well as exclusive designs.
http://www.jakpumpkin.com

Just Collecting Dust
Includes a variety of vintage metal and vinyl, as well as a collection of thermos bottles.
http://www.justcollectingdust.com

Lunch Box Collector
Features a price guide, trading post, cleaning information, historical information and images of boxes currently available for sale.
http://www.lunchboxcollector.com/

Lunchboxes.com
Offers Thermos brand, Igloo, Nissan steel, insulated soft, hard plastic, and metal.
http://www.lunchboxes.com

Nelson's Metal Lunch Boxes
Collector selling vintage metal, plastic, and vinyl lunch boxes and thermoses. Includes image gallery.
http://www.nelsonplain.com/