Ok so heres how some of my games against protoss go... They start by pumping out several gateways, so I build a few lashers and zergling... this keep off the early zelots. I then change towards a hydra/roach/ling combo to deal with a growing land threat of zelots/stalkers/sentry. I might grab a few infestors for surport too. Then the dam colossus turn up. 1 - 4 is just about dealable with, a bit of focus fire and there dead before the cause too much damage. But when there 5+ up and running then my gound troops are in serous trouble. Now I guess the soloution would be to get a strong air up, but I can't seem to react fast enough and air units cost alot of gas.... and they deffently be low on the upgrades. Any tips?
I wouldn't say 150/100 is a lot, and corruptors are useful all around because of corruption. And neural parasite works wonders on colossi. Make sure you have plenty of lings or roaches to keep stalkers from getting close to the infestors. Alternatively, you may opt to go for mass roaches - that works as well and is somewhat easier to pull off. Especially if you flank with a couple of them as colossi are usually kept at the back, out of harm from the front. And remember to upgrade carapace - they give double the protection against colossi and zealots.
Against protoss i usually use mutalisks.. they are very effective against their ground units since only stalkers hit them for 10 damage each... Plus you can harass them a great deal