I wrote a simple script that parse the module's page and install or update the most up-to-date version.
This works for themes as well. To use it, simply go into a modules or themes folder and run one of the tool.
Valid folders are:
However, not that you should not try to update root folders, they are reserved for core modules and are updated with Drupal.
drupal-install-module.sh will install or update one module, drupal-update-modules.sh will batch update all modules in current folder.