My partner and I played a bunch of Starcraft 2 games today on the 2v2 ladder, and the strategy we were trying out was a 10pool early aggression by Zerg (me) supplemented by whatever early Zealots my Protoss ally could afford to send without hurting his economy (usually 3-4), and do as much damage to our opponents as possible. The usual result was to kill a Protoss pylon, slowing down his Gateway units, killing a Queen, reducing the Zerg's ability to spam Zerglings in defense, or to kill all a Terran player's marines and force his SCVs to come off gathering to defend.
The key Zerg tactic was to keep the first 6 Zerglings alive for as long as possible, doing as much harassment as possible (this means you have to hotkey your Hatchery and try not to go back to look at your base for more than an eyeblink, for either upgrades, making buildings, or moving drones to/off gas). When the second wave of Zerglings arrived, you could take on even a lone Zealot or 3-4 marines, and then go on to harass workers some more.
If you want to see what build I used, please go see my 2v2 10 pool article.