2v2 is EXTREMELY gimmicky, and matrix dependent. There's no justifiable reason to not run a druid if you're starting from scratch. If you're just in it to win it, go with a warrior for the other. 8/10 of the top teams on Bloodlust are that combo. Rogue is another good one, but requires a pretty significant amount of micro, even compared to warrior. Warlock/x mana drain & attrition dies next patch, so I don't really recommend that build. Two DPS insta-gib teams are fun for lower brackets, but extremely difficult if you want to go higher. (duelist/Gladiator)

In 3s, if you want to run a single class, you could run 3x resto/ele shaman, with the new healing -> spell damage changes, that will be a very potent team, I think.

3x frost mage might be fun, but I don't know how well it would work, you'd DR yourself out of FN extremely fast. You absolutely can not take frost bite though. Silence DRs now, so you'd probably be better off running 1 or 2 of them as 17/0/44, and one as 0/8/53, and pick up full winter's chill. It'd be hit or miss, but with elemental + chain Freeze + IL + CoC spam, you could probably insta-gib a lot of teams, especially 2 healer + 1 DPS, which seems to be the FOTM.