As we are allowed to mention worldcoingallery.com then I see they have a companion site ...
http://worldbanknotegallery.com/
and there is a list of all countries, and on their coin site a link in the list is clicked on to view images. The banknote site is different, in that a small camera icon is hovered over or clicked instead. There are also some pictures, on a 'Click here to view design examples' link at the end of each country list; their quote is 'Gallery Total: Over 26,000 banknote images from over 300 places'
Both sites have good lists.