ClickPic lets you quickly resize, rotate and flip images, and convert them from one format to another. It has an incredibly handy batch image file renaming function, so you can quickly give meaningful names to all those horribly-named files that you get from your digital camera. And, if your camera records orientation/rotation information, ClickPic can automatically rotate the image to the correct orientation. And it does all of this from Windows Explorer. 14 day free trial for Windows.