iBrowse - description from Softdepia.com:
iBrowse uses the familiar concept of Windows Explorer (TM) to make browsing, storing and manipulating your images as painless as possible. Transparent thumbnail display allows you to quickly and easily locate the images you require, whilst true background processing ensures extremely good performance. The use of optional personal "albums" for image storage keeps your images away from prying eyes. Favourites let you store shortcuts to locations where you regularly browse for images, for example an Internet download or cache folder. This really is a "must have" tool for any image collector.
iBrowse is a "Free to try" program. You can download and try it for an evaluation period.