This strategy works best on 'TheFastest$$MapEver!' (I believe that's the name) My friend and I have used this about 25-30 times the past week on 2v2 games, and only lost once.

Start by building a total of 9 drones, on the 9th drone, build a spawning pool. After the drone begins to make the pool, build another drone. By the time the second 9th drone is out, you should have 200+ minerals (more if you are using the map I stated above) have that drone build another hatchery. Build another 9th drone, and build your third hatchery. Your spawning pool should be done by now, make 1 drone and 1 overlord. Have the drone mine minerals, and after the overlord is out, make a few zergling. >IF< you are getting rushed, it should be a very small amount of units, so your three hatcheries could easily build enough zergling to fend off the attack. Now you have 3 hatcheries, continue building overlords and zergling (Only need about 5 or so more drones) and once you get 24+ zergling, your opponent is ready to die. If done correctly, you'll easily have far more zergling than they can handle, and since you have three hatcheries (four if you decided to build another) you can easily reinforce your first attack, so continue the push until they're dead. If you find they AREN'T dying, continue making zergling while building a few drones, making a few extractors w/ 3 drones in each one. You can start building a hydra den, while continuing to pump out zergling. After the den is done, start making only hydras. Your combination of zergling and hydras will be extremely hard to beat.

Remember: Don't build your 4th (or more) hatcheries too soon, make sure you have at least a few forces to defend just in case. Since this is zergling only (for the most part) minerals will not be much of a problem, 15 or so drones should easily be able to fund this attack (especially on TheFastest$$MapEver map), if you get into the hydra stage, just add a few more mineral gatherers and 9 or so gas gatherers.

CreepColony's Opinion: A pretty good strategy, also works well on non-money maps.