Nabisco's Famous brand cookies are the standard for this recipe. They're super-thin chocolate wafers. My local grocers always carries them either near the butter/yogurt case, or the frozen section, in a display with other popular cookies to use with desserts.

I make this ALL the time!

Mr NL MVP likes to do this in Cincinnati. His first big league HR was against Cincy in early June 2010 (the 9th?). He put it well into the upper deck that day.