The crop-and-resize tool in Photoshop is one of the few features that I use all the time but I haven't been able to figure out how to do it in GIMP.
Photoshop allows you to set a size for the final image, say 100px square, then click and drag to select an area of the image. It keeps the aspect ratio of the selection fixed and automatically resizes it to 100px square when the crop is applied.
In GIMP, setting a fixed size of 100px square results in a fixed-sized box. You can't resize it, so you're forced to first scale the image down, guessing what size would be most appropriate for the crop you want to achieve.
If I'm cropping images for the web, this is a real pain.
Seriously, hasn't anyone written a plugin or something to make this easier? I keep coming back to GIMP once a year or so to see if it's been added, but so far it seems like it's still absent.