AndreaMosaic - With AndreaMosaic you can create your own photographic mosaics made with your own pictures.
PixBuilder - Free Photo Editing Software for PC
WidsMob Montage - Make stunning mosaic photos or montage shape with tiles, which supports both JPEG and PNG files.
PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
Mosaic Creator - Mosaic Creator is professional mosaic tool. You can create your own picture mosaic.
Fotografix - In addition to being totally portable, Fotografix has a ridiculously small footprint.