Pokescope
This mini-viewer can view small cards and large cards and computer images... it works with any stereo image size.
Pokescope 3D Viewer Named Best
Product available for purchase and most useful for ISU (International
Stereoscopic Union) members!
You can:

View full-screen, full-color 3D images on
your computer
View large print stereographs
View 4"x6" stereo prints without cutting
and mounting
Browse traditional stereo cards
View full-color stereo on TV screens
Features:
Glass prism windows for a clear view, low
distortion, and easy cleaning
Durable ABS plastic construction
Folds into a protective shape which easily fits into a pocket