For years, Westcott has made some of the best modifiers out there. They’re well known for their Apollo softboxes designed for speedlites. However, they also make many umbrellas. I purchased a three umbrella package where I was able to obtain three 7-foot parabolic umbrellas for a very affordable price. And to date, my most used umbrella is the silver interior version due to the extra punch that silver gives to the specular highlights on an image.
But man, do you need some powerful lights to take advantage of the size.