Vostok ice core data.
Just do a google search. There are tons of graphs for it.
One of the problems is that these graphs do not reflect the current level of CO2 such as the following related graph does
http://www.clearlight.com/~mhieb/WVFossils/last_400k_yrs.html
or
http://en.wikipedia.org/wiki/Image:Carbon_Dioxide_400kyr-2.png