Does anyone have any ideas or suggestions as to what ED-E actually 'says' during his end slide? There's probably no actual way to find out what he says, but it would be rather interesting to know. Speculations welcome.

I was woundering the same, if anyone knows please share

If you have subtitles on, you can read it. As usual, check http://fallout.wikia.com/wiki/Fallout%3A_New_Vegas_endings#ED-E for spoilers.