Okay… here's the deal. I personally believe that on-camera lighting modifiers are amazingly overblown by the marketing departments of various photography companies. They all claim to do incredible things with the flash on the camera, but every time I test them… they all turn out about the same.
There are definitely times when on-camera flash is the only option available to a photographer. For example, a wedding photographer who is shooting the guests at a wedding reception simply can't set up off-camera flash to shoot each moment as it happens during the wedding party. More than likely, this type of photography will require the photographer to mount the flash on the camera, throw on a basic on-camera lighting modifier, and shoot away. It's quick and dirty photography.
I have tested quite the number of on-camera flash lighting modifiers and every time I put the photos head-to-head against other on-camera lighting modifiers… the results are about equal. In fact, I bought a $50 or $60 Gary Fong Lightsphere and used it for several months and then got suspicious that the oddly-shaped contraption really was doing nothing more than if I just put a piece of tupperware on my flash. So, that's exactly what I did, and in this test you can see that the Gary Fong Lightsphere performed no better than Tupperware in my opinion.
So, I think there are really only three things you need to look for in a lighting modifier: (1) Choose one that is inexpensive because the costly ones just don't seem to produce better results in my opinion, (2) Select one that won't get in the way of your camera or be too cumbersome. Remember, it's quick and dirty lighting here. (3) Find one that is somewhat versatile and allows you to bounce light, reflect light, etc.
With those criteria in mind, I think there is really only one good option here… (and no, nobody paid me to say that)
As far as on-camera lighting goes, the Rogue Flashbender from ExpoImaging is the creme of the crop. I had heard of the product before, but I hadn't tried it until Dustin Olsen showed me one while we were filming video tutorials for our online portrait photography class. It's just a little more expensive than I'd like, but it is incredibly versatile, easily portable in your camera bag, and gives good light quality due to the array of versatile setups you can do.
The flashbender is basically a large flat piece of material with bendable rods inside it that will allow the photographer to bend it into whatever shape you want. It straps onto the flash easily and allows you to bend the light to shoot anywhere in the room, or you can use the diffusion panel to create a miniature softbox.