Here is an interesting comparison of Cortana over the course of the 4 halo games:
PTesh adds his dulcet prepubescent tones over the top of one of the new trailers for weapons...
Try upgrading your browser to Google chrome (you wont regret it). There is probably an IE...
On the multiplayer level "Spire" you can use the various tricks to get out of the map in theater mode to view this easter egg. Once out of the map you can go to the bottom of the level and you will find a strange green shield with the reach emblem on it. The shield is inside a solid cube, but once you are in theater mode, you can still see it clearly.