ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
Placemat - Pretty nice placeholder images.
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
PlaceKitten - Dead-easy placeholder images. Of kittens.
Batch Image Resizer - Resize, crop, shrink, flip, exif-rotate, convert, enhance, process multiple pictures and photos with professional software! 120+ Actions, 30+ Image Formats
placeholder.pics - Lightest way to include placeholder images in your design