A great build is the Roach + Hydralisks build against Protoss with a mix of corrupters(against collosai). Hydralisks are very good against every single gateway army, and roaches will soak up damage and also do a reasonable amount of damage. If the enemy decides to you collosai, don't panic, just get some corrupters. If you can't make any corrupters, use your roaches to burrow under the collosai. You always want to get the hydralisk range upgrade to make them immensely powerful against air units and gateway units.
Another wonderful build is the "MutaLing" (Mutalisks + Zerglings). This is a great build because both units can move very quickly. Just make sure to get the zergling metabollic boost upgrade. This is a great build because zerglings can surround enemy forces and they are very inexpensive and fast to make. When you surround the enemy and attack with mutalisks, the enemy won't know which to attack first. The AOE unit with a lot of damage, or the speedlings that attack quickly. If you lose all your zerglings, just make more with all the larvae you have.
My last build would be the "spanishiwa" build. It is know to have great affect against all races. In order to do it, you make spine crawlers and queens at the start of the game for static defense. You get a quick expansion and get 4 gas at the same time. This will get you a lot of gas and you can get lair very early. The queens and spine crawlers will do a great job defending as long as you have about 4+ queens to heal themselves as well as the spine crawlers. This build is great to get a good economy.
