Newer versions of Groovy (1.7.2+) offer a JDK extension to more easily traverse over files in a directory, for example:
import static groovy.io.FileType.FILES
def dir = new File(".");
def files = [];
dir.traverse(type: FILES, maxDepth: 0) { files.add(it) };
See also [1] for more examples.
[1] http://mrhaki.blogspot.nl/2010/04/groovy-goodness-traversing-directory.html