Red Verses Blue - Blood Gulch
Check out this fantastic online animated movie series, BLOODY FUNNY! Its free to download the low res videos and a new one is released every couple of weeks. They use the Xbox Halo engine to animate the characters which I believe they got an award for last year.
They are currently well into the second series and unfortunately you can't get all of the first series but you should be able to jump in from the start of the second without to much trouble.