Famous statistician John Tukey (http://en.wikipedia.org/wiki/John_Tukey) created the boxplot in 1970. Boxplot shows a distribution summary in a small amount of space. In this paper [PDF], Hadley Wickham and Lisa Stryjewski look back on boxplot and its evolution up to present.
Boxplots are particularly useful for comparing distributions across groups. I was introduced to them two years back and have been using them ever since.
I think Boxplots are perfect example of what John Tukey believed
Its far better to have an approximate answer to the right question, than the exact answer to the wrong question…
Oh by the way, excel 2003 donot have boxplot by default so I have created a excel VBA code to just produce boxplot in excel. Do check it out!