V’Ming Chew has an interesting article on building an arena team at WoW-Insider.

He focuses on class composition, particularly examining the class representation of the most successful arena teams and also a breakdown of four traits needed to be competitive in arena: damage, heals, control and durability. In 2v2 particularly, durability is important (so Wise & I setting up a 2v2 mage / priest team might not be the best plan ). He then examines the group compositions of 3v3 and 5v5 teams. Well worth a read for arena fans, especially as it has pretty pictures