I just finished this Small map. It works with all CTF varients, Oddball, Assault, and obviously Slayer and team slayer.
It's good for 4-8 people. It's a symmetrical arena style map. I've tried it quickly with MADbull, but I'm very confident that it will be wicked fun with full teams.
http://www.bungie.net/Online/Halo3UserContentDetails.aspx?h3fileid=70355639