Dimensions 2 Folders is a portable tool for organising images by height, width, aspect ratio and more.
At its simplest you could point the program at your Pictures folder, and have it copy the contents into new folders named after their resolution. You'll get multiple folders with names like destfolder\1920x1280 and destfolder\1024x768, each one containing images of that exact size only.
It's also possible to sort images matching specific resolutions only. You could ask the program to look for 1024x768 and 2590x1920 pics, for instance, maybe with tolerances of 128 pixels to catch cropped images or anything you might be able to use.
You're able to sort images by aspect ratio, the total number of pixels (width x height) and more.
When you're ready, select a destination folder, make sure you're copying the files rather than moving them (unless you're 100% sure you know what you're doing), click "Go" and your images are reorganised in seconds.
Dimensions 2 Folders is an easy-to-use and convenient way to organise your images, but it doesn't have all the features you might like. There's no way to save particular sorting rules, for instance, or preview the results before you move any files.