OK, here it is.
~Link~ This is my old one for my first book. I haven't been using it during my current edit.
It's not very exciting, but it did the job for me.
So basically, you stick a date in column A. Total word count for your book in Column B. Chapter number/description in Column D. Column C is a calculated number of words written that day. (Can go negative; that happened with me while I was editing and pruning stuff out.)
In Column F, you also stick your chapter number/description, and then Column G calculates total words for the chapter, while Column F calculates the last date you fiddled with the chapter.
Then there are the two graphs I mentioned. This spreadsheet has the flaw that if you change the word count in more than one chapter on a given day, which means you need to add a couple of rows to the A, B, C and D section, the bar chart only shows you a bar for one of your entries. But oh well. The total word count stays accurate.
Yes, I'm a nerd :P.