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...
Invisible Elite with Data Pad
Level: Noble Actual
At the very start of the level when you hop out of the falcon, if you sprint down the hill you will spot an invisible elite carrying a data pad. If you kill him you can pick up the data pad. He runs down the hill and once he reaches a certain point he just disappears. He is carrying one of 19 Data Pads scattered around the campaign. Now even though these are more of a Terminal or Audio Log than an Easter Egg. You should go and check these out. There are more Easter Eggs about the Data Pads further down the list.
Good Hunting! ;)