Cadence: http://www.cadence.com
Free Allegro Viewers (15.7 & 16.2+)

Valor: http://www.valor.com
Free OBD++ Viewer Tools

GC Preview: http://www.graphicode.com/GC-Prevue_Gerber_Viewer
Free Gerber Viewing Application

Solidworks: http://www.edrawingsviewer.com/
Free DXF 3-Viewer