Wow! What a great thread. I don't know how I sometimes miss these threads when they are first posted, LOL.
The problem with wormers is that not very many of them get all worms. This is not necessarily
that big of a deal anyway as most vets (or at least all of the vets I have worked with) recommend rotating wormers anyway. Ivermectin is great. I have used it for many, many years, but it does not get tapeworms or even all round worms. Safeguard (Fenbendazole) is great too, but it also does not get tapeworms.
As someone mentioned early in the thread, Flubenvet (Flubendazole) is awesome, but it is hard to find in the US. There is another wormer that a few people here on BYC recommend called Valbazen. Like Flubenvet, it is supposed to be very comprehensive. As luck would have it, they had a big bottle of it at my feed store that I was able to get for a great price. I am going to try it, but thus far have no personal experience with it. The other option is to, as I already said, rotate wormers. Most vets recommend doing this anyway. In actuality, people experienced with the Valbazen recommend to use another wormer like Wazine prior to using it as well (Wazine is really cheap and easy to find).
A lot of times, wormers can be found locally. If not, I sometimes purchase various things also from First State Vet Supply. A lot of BYC'ers use them. They are operated by Dr. Peter Brown, whom is very experienced with poultry medicine. I'll paste a link below to their wormer page. HTH!
http://www.firststatevetsupply.com/store/index.php?cPath=23