stuff.alienbill.com/amazonadder/ - Amazon has a thing where you can request an "Order Report", a CSV of all the stuff you've had shipped over the years (oddly, there seems to be no equivalent for digital orders.) Anyway, you can pull the data from them into a spreadsheet program, or if you're not so clever with spreadsheets, you can copy and paste the raw data into this new webtool I made. (All calculations are done inside your own browser, nothing is sent to any server)
The page gives you a chart of what you spent in each category per year, then a breakdown (sorted by total spent) by year, by month in year, and then by category where you can zoom in to total-sorted lists of what you bought.
My totals? Since 2004, about $16K. Trend definitely upwards - 70% of that's in the last three years. On the other hand, December is the biggest month for spending, so some big chunk of that is gifts.
Sigh, here's my top categories:
Personal Computers 1145.85
Video Game 1074.34
Paperback is around 1000 (hard cover is a bit below in the list, around 500) I really do wish Amazon included Kindle download data!