I love some of the classic Halo 2 remakes that some people have done, such as Halo 2 Ascension, Lockout, and especially Zanzibar! Great for Slayer or King.
And to add to what is said above, Coldsnap is a pretty fun CTF/Slayer map. But on second thought, CTF would take a while. It would be almost impossible to finish with people who actually knew how to play CTF well, unlike some people in other Coldsnap servers in CE.