At times you may have the requirement for minimizing many photos at once say if you want to upload many photos on facebook, or when you have to send many photos via one e-mail. You can use photoshop to do the batch resize but it is a lengthy and cumbersome process. Instead, you can try the Image Resize Powertool! Shrunked is also a good upload-on-web specific tool which you can take a look at (Available as Firefox extension).
To use this tool all you need to do is select the set of images that you want to resize at once, and right click on one of them, you will see an option called "Resize" on the menu that shows up, just click on it and you will be presented with an advanced options box that has options for setting image dimensions. You can see this screenshot below.