JuiceAnalytics write about lightweight data graphing. I instantly love the idea and I used it in a chart I was working on just recently.
General idea is to put a bar chart right there in an Excel cell. Just use REPT(text,number_of_times) function to repeat desired character, for example | or X or maybe O.
There are several interesting directions in which you can evolve this idea and use conditional formating, some ASCII art and so on. Just see for yourself!
Now this is a fantastic idea! I really like simple and effective tricks and I love visualisation. This is both.