App for Cropping and Resizing an image
But of course Preview!

To resize: Choose Tools > Adjust Size, then enter the size you want to change the image to, then click OK

To crop: Click the "Select", then click and drag to select the area of the image that you want to retain. Next, choose Tools > Crop or press Command-K. If you crop too much, you can press Command-Z or choose Edit > Undo to undo the crop.