I can only imagine the hilarious combinations that can be made if people party up and collaborate lol. These are all tested and are A-OK by 343's standards, so enjoy!
A lot of those are blocked for being offensive. Or they were in Reach, so I assume they still are at least.
Aside from the obvious 4 letter words that are blocked I know JEW (and any variants), NIGR (and any variants), YANK, and anything racial or possibly xenophobic was blocked.
Also FISH, PIPE, SONY, PS3, and a couple other totally random ones.
Well I just tested literally every single one of those yesterday and they all work. SONY and PS3 are allowed and JEW is definitely allowed as it's not inherently offensive. One could just be exhibiting Jewish pride or something. But NIGR is blocked which is why I have a few variations of it in my post.
EDIT: Some more tags: GANK (gang kill), FNG (F**king new guy), USA ('Murica), HICK, JHAD/GHAD (Jihad), PAKI, ARAB, 2 G 1 C (Two Girls One Cup), BICH