Lightbox 2.0 Free version is a limited version of Sagelight 2.0. It features the same UI and easy-to-use Quick Edit Mode controls.
If you just want to adjust your picture and make it look great without all of the extras of Sagelight, then Lightbox 2.0 free version is a good choice.
Lightbox 2.0 Free version has earned awards (see the main page), and contains the same core real-time engine of Sagelight, allowing you to control many different aspects simultaneously, giving you an intuitive feel for editing your image.
Lightbox is free, with no strings attached. It is no longer updated, however. Please see Sagelight below.