SheetMetal.Me
SheetMetal.Me is an excellent resource for sheet metal engineers and designers with plenty of articles about terminology, equipment and processes related to sheet metal fabrication.
CustomPartNet.Com
CustomPartNet.Com hosts an excellent array of sheet metal related calculators. Bend Allowance, Spring Back, V-Bend Force, Wipe Bending Force and Deep Drawing Force calculations are made easy to understand with clear inputs and reference pictures. While they don’t expose the underlying equations they are still a big help.