The problem with the whole preventative discussion is that for some worms once you know they have them it may be too late. We just recently lost our oldest hen to Gapeworm, by the time she displayed symptoms they had already infested her windpipe, but like the vet said once she gets to this stage it's too late.
I've read these boards about recommendations for dewormers and some of them are only available by prescription. Someone mentioned Wazine, I read the label on that last night (Warning: Not for use on chickens that produce eggs for human consumption). If they don't want us eating the eggs, why would I want to feed it to my flock.
I'm also looking for a less harmful method to treat worms (I won't say natural because arsenic is all natural, but I wouldn't feed it to my chickens). I'm about to try Verm-x and will let everyone know my results. As for ACV, although many say it's a good dewormer i have to agree with the comment that once it's diluted it's ineffective, but I know that it's more of an immune booster than an actual dewormer which may help with the chickens own system to fight off infestations, just like Yogurt is good for their digestion.