I've been using Benefiber as my main fiber supplement for a little over a year at the time of writing (January 2008). Each serving is 2 teaspoons and has 3 grams of fiber. You can take up to 3 servings a day to get 9 grams of fiber total.
I had just gotten over a particularly bad hemorrhoid flare-up that didn't have me walking straight for about 2 weeks. So I decided to take a fiber supplement to try and prevent future flare-ups. I chose Benefiber because I had seen plenty of commercials for it, so I was familiar with it and it looked more appealing to take than Metamucil.
Benefiber dissolves pretty easily when mixed with beverages, though you may get a few flakes floating around the glass. I've also used it in a couple of pasta dishes, mixing it into the tomato sauce before popping the dish into the oven to bake. The Benefiber powder is tasteless, so you won't be able to taste any difference in your dish or beverage.
I've also tried Fibersure (due to the higher amount of fiber per serving), and I prefer Benefiber because the mixture dissolves more easily in my beverages, which is how I usually take these fiber supplements in powder form.