GIMP is versatile and flexible enough to transform from laggy and clunky into a fast and efficient powerhouse; all it takes is a few minutes of extra setup. GIMP felt clunky until I changed these ...

In fact, Joe Eitel of DevHardware.com says GIMP has about 150 filters and effects. If you want more, it's also easy to add plug-ins to GIMP's Plug-ins folder and brushes to its Brush folder.