You could try PhotoToolCM (third from the bottom) it adds an option to the contextual menu and allows for batch resizing (i.e. right click, scroll down, photo tool, resize), super easy and free!
ImageWell is very good. Just drag and drop image files (not RAWs) and it outputs resized images. If you don't have many files to do then the shareware version is probably fine. If you need to actually do batches, then the registered version will do that for just $15 bucks.