MrZoogle
On wunderground, you can set a custom date range to look at, and then at the bottom there is an option to get a CSV download.
For instance, here's a link to historical data for 2012 YTD data for London.
http://www.wunderground.com/history/airport/EGLL/2012/1/1/CustomHistory.html?dayend=24&monthend=5&yearend=2012&req_city=NA&req_state=NA&req_statename=NA&format=1
From the web page that appears, copy the data to XL, and then do a Text-to-columns, comma as delimiter.