Flash

For anyone that is looking to expand the capability of their Holga by adding an inexpensive flash unit to their bag it looks like this one might be of interest. It is powerful, has a built-in slave, and cheap compared to the major brands. Although the reviewer experienced some quality issues, it might be worth taking a look at the Yongnuo YN-560.

http://strobist.blogspot.com/2010/08/test-drive-yongnuo-yn-560.html