Only Wiz and Dru get ports. The others mentioned can only gate themselves.
But yea, Shm would be my first pick, and DPS for other. Druid could fill DPS and add ports and back up heals, and 0% rez later on with AA. Wizard would also be excellent DPS and ports.
Enc would be handy, but their buffs are pretty long other than Haste, which a Shammy could do also, just not as good, but if your melee have good worn Haste and near max stats, the Shammy's will be just as effective, and the Shm slows are better, and their buffs don't last long. Also, they add alot of melee DPS with their short buffs, helping out the Pally, Bard, and pets for those with Pet Affinity. Also, as others mentioned, the Bard should have crowd control tasks handled.
Many classes could fill the last spot tho. I'd say it depends on what the group needs the most. Necro would be good for DPS and can feed mana to the group, if that's a problem. Also could help pull really crowded area with FD, bringing the number of mobs down to something the bard could easily crowd control. I mentioned Dru and Wiz also. Dru will add HP buff with mana regen, which will most likely help most of the group, other than the bard.
I'll stop with that, eventhough there are lots of other possibilities, especially if you PL some toons, just to buff the rest of the group and not actually be active members of it.
Yther Ore.