I have both the "Round Stainless Steel Lunch Box - With Dish" and the "Stainless Steel Lunch Box - Rectangular" from Pearl River in New York. They are sturdy and inexpensive.
You'll need to browse the 6 pages (look at pages 2 and 3)- can't get individual pages to link: http://pearlriver.com/v2/FramesCat.asp?iGroup=333

Three sizes of each, from $4 to $7.