This could be real old news but I will share it just "in case".
The latest version of the free image viewing and editing
software called IrfanView is version 4.0 and with an extra
Plugin called "iv_formats" it can be used to view RAW files.
The speed to browse is really impressive compared to other
viewers, especially if you set it to use the
embedded preview
and the
load half size image as options on the PlugIns tab.
I have checked it direct from the SD and it can flick through
full screen images from 10.2 Mpx Nikon NEF in less than half
a second per image.
It also lets you delete or open your choice of editor or even
resize as you browse. I know that IrfanView has been very
popular for a free JPEG viewer but this RAW Plugin makes it
a very useful tool for digital photography.