Google Picasa is best application for Managing stock of images. Google Picasa not only allows your to preview images but also lets you to create albums, collages, export as html pages, apply effects to images, batch edit and much more.
Here is nifty tool Picasa independent album exporter to export albums created with Picasa as jpg images. You can download all your albums uploaded on picasaweb and using Picasa Independent album exporter you can export these albums as jpeg images.
Screenshot of Picasa Independent Album Exporter