PC

Graph-X Viewer - View, convert, and create image thumbnails.

Express Thumbnail Creator - Quickly and easily prepare your image collections to be published on the web. This smart and handy tool creates high quality thumbnails, organizes them into web pages and links to full size images. It can also resize and modify the original images.

Easy Peg Thumbnail Creator - Create Photo Galleries in HTML with the EasyPeg Thumbnail Creator

STGThumb - Allows you to quickly make high-quality thumbnails.You can convert from several formats (AVI;GIF;JPG;TIF;PNG;BMP;etc). Outputs to JPG. On animated GIFs and AVIs, you can get thumbnails of the first frame. Option to auto-rotate images to get a better fit.

MAC

ThumbsPlus - Thumbnail creator for the Mac