In Halo 3: (these are definitely correct)
Killing Spree, Killing Frenzy, Running Riot, Rampage, Untouchable, Invincible
In Halo 2: (I think these are correct)
Killing Spree, Running Riot, Overkill, Rampage, Untouchable Also an Halo 2, between 20 and 30 kills in a row, the announcer will say "Un-Freakin'-Believeable!" Though this is for entertainment only and no medals are awarded.