These are excellent, the Rick Roll part in COW4 (that's a neat abbreviation) is still hilarious.
As for further ideas, I could imagine some more TF2-related bits. For instance, the AE Bad Ending, with the bottle smack, paired up with the Demoman's
line upon a melee kill, along with the sound of the bottle smash. Also, Abe getting past minefields while being chased by flying Sligs would also be neat ground for some
Bonk! lines from the Scout.
Just to name a few. But I can come up with a dozen more, if required!