If you constantly post your photos on the web, resizing them can be a bit time consuming. Some websites now do this during the upload process, but this does seem to slow it down.
DropResize is a beta application that sits in your system tray, quietly waiting to resize your photos. It currently only supports JPEG images, but it's a pretty neat idea. When you first open the application, hit browse to choose a photo folder. Once this is done, any images dragged into that folder will be resized to the width or height you specify (ratio is kept the same).
DropRezise is still under development so may be a bit unstable, but so far it has performed fine for us. It makes resizing really easy. There aren't many options, but perhaps that would be unnecessary!
DropRezisemay be in beta, but it's already a nice app for quickly resizing your photos, assuming you use JPGs.