Horos - A free, open source 64-bit DICOM medical image viewer
Weasis - Weasis is a multipurpose standalone and web-based DICOM viewer.
MicroDicom - DICOM viewer. MicroDicom is a free DICOM viewer. Export to the most common picture formats, movie, clipboard. It is equipped with most common tools for manipulation of DICOM images.
IrfanView - IrfanView ... one of the most popular viewers worldwide.
3DimViewer - 3DimViewer is a 3D viewer software for medical DICOM datasets that is written in C++, effectively runs on MAC OS, and Linux systems.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!