Field as Block is a lightweight module that allows you to display a field as a block. The same results can be achieved by using Panels, Display Suite or custom code but this module offers a lightweight alternative.
CCK Blocks offers similar functionality, however on the project page they recommend that you use Field as Block for new projects. It looks like CCK Blocks will be deprecated in favour of Field as Block. For more details read issue #1920636 (comment #4).