I play on a 3v3 and 5v5 squad that are doing well.
Setup is:
Disc\Holy Priest
Enhancement Shaman
Warlock
Disc/Holy Priest
Enhancement Shaman
MS Warrior
Retadin
Rogue
The 3v3 actually went 7-3 this past week, and I missed our 5v5's games >.< but last week we went 20-6 and raised my PR nicely.
The Disc Priest is huge for enhance because they just spam mass dispel and all those annoying barriers to your fist weps just vanish, pop Blust, Shammy Rage and Trinket and goto town on some poor healer. Pour on the Purge on BoP or whatever and blast 2-3 opponents down as fast as possible. Melee in Arena is sick and yet sometimes we still like to sub in a Frost Mage for the Retadin in the 5s which allows for a bit more CC against 2 healer squads.
Just remember to do your part as a shaman in arena. As my Arena teammates tell me: Pop yer lust, man, don't forget the lust.