WinCDEmu is an open-source software that allows mounting CD/DVD images by clicking at the image files in Windows Explorer. It supports all Windows versions from WinXP to Windows 7, is open-source and completely free.
WinCDEmu makes mounting CD/DVD images simple: double-click on an image file in Windows Explorer and a new drive letter with the mounted image will appear. You can mount as many images as you want at the same time, and you don't need to reserve drive letters when nothing is mounted. WinCDEmu supports ISO, CUE, NRG, MDS/MDF, CCD, IMG formats and runs on all Windows versions from WinXP to Win7.
To unmount an image, double-click the corresponding file in Explorer again, or simply eject the corresponding CD drive using the context menu.