QuickView is a free portable photo viewer which uses assorted software tricks (reading image data in advance, displaying pics using OpenGL) to show pictures with the best possible speed.
The interface is minimal. Select or drag and drop a starting folder or archive, the program displays the first image and you can step backwards and forwards using the keyboard or mouse.
Viewing pluses include support for several RAW file formats. There's also the ability to display two images at once, one to the left of the screen and one to the right. This is supposed to help you view pages from a comic or other printed document, but could have other applications, too.
The program offers multiple scaling options and methods to ensure the best combination of quality and speed.
Right-clicking displays more functions, including the ability to copy the image or the file to the clipboard, move the image to the Recycle Bin or display EXIF information.
QuickView is easy to use, and its speed and RAW file support are pluses. But it was also unreliable for us, crashing a few times, and the interface needs work.