I know that you can get daily traded volume BTC price on Bitstamp from:
https://bitcoincharts.com/charts/bitstampUSD#rg60ztgSzm1g10zm2g25zv (click on "load raw data" at the bottom of the chart, and it will show daily traded volume for the past couple of months (maybe 60 days?)
It is possible to calculate the monthly weighted average from the days. You multiply each day's volume by its price. Then you sum all those products. Then you divide this figure by the total volume for the month. It works out to $11,615 USD which is within a hair of Phil_S's data.
Maybe I should add this at the end of each month to the top 100 list?
Thanks for that description about how to get to that kind of a weighted-average number for the monthly, yefi. Your description makes sense.
I agree that the monthly weighted average does seem to be an interesting calculation that could be added to the top 100 daily listings (but then it is no longer merely daily), if you believe that you can do it in such a way that does not clutter the ability to digest the information contained in those updates. Alternatively, there could be a sister thread that would have monthly or some other timelines, weekly, quarterly, yearly... where do you stop?
Of course, when you add any of those kinds of features (or extra data points), you are adding work for yourself, but the rest of us tend to benefit from being able to look at running tallies like that to the extent that we can understand what those kinds of numbers mean... which is probably a continuous challenge to present information in such a way that even newbies are able to get some meaning from the information that is presented without getting caught up with too much information.
Even that top 100 daily information is a quite profound kind of information that newbies might not understand by merely looking at it, but you do have links that describe how the numbers are calculated, which is likely helpful to those who are willing to try to go to the next level of understanding of the information that they are viewing.