If you need quick and dirty image adjustment, and don't want to load iPhoto or even a shareware application like GraphicConverter, you can use Preview.
You can crop
Adjust image properties such as hue, saturation, exposure, brightness, in fact all of the same properties as from inside iPhoto
and others such as resize.
These features and the ability of Image Capture to download selected images means quick for some jobs you just don't need iPhoto or Photoshop. These tools load quickly, are very lightweight and take very little RAM.