For Windows users, I suggest IrfanView:

http://www.irfanview.com/

It's freeware (though not open source) and an excellent and fast image viewer. You'll have to also download the plugins to view the Dicom images (the MRI images). Fortunately all plugins for IrfanView can be downloaded as a single file as explained at the site above.

As other have already mentioned, the MRI images are full of personal meta data (which can be shown by clicking "info" in IrfanView). I assume that the OP must have been aware of this.

OsiriX [1] is a popular OS X/iOS viewer.

3DSlicer [2] is an excellent alternative that runs on Win/OS X/Linux

[1] http://www.osirix-viewer.com

[2] http://www.slicer.org

On OS X, Horos is a free and open derivative of OsiriX.

http://www.horosproject.org

DWV [1] (open source, Flash/Java-less webapp) Seems to still be a WIP, but it lets you load the files from the repo (to localstorage), despite throwing errors left and right. ;)

[1] https://ivmartel.github.io/dwv/demo/stable/viewers/mobile/

Hi, I'm the author of DWV. You're right still WIP and happy to help solve errors! Pull requests are welcome!

I downloaded Osirix, it is the most complicated process I ever seen.

Found this fork that seems more open

http://bettar.no-ip.org/lxiv/