I know that the plastic flash cap (such as the
Sto-fen Omni Bounce cap) isn't popular among Strobists (ie. photographers who use a lot of flash), but I've had pretty decent luck with this plastic cap, both for indoor flash pictures and outdoor flash pictures.
I know the principles behind creating softer, more flattering light from a flash: the larger "apparent size" of the flash (such as bouncing the flash off a wall or ceiling), the softer the light falls on my subject. All the flash modifiers mentioned on this thread help to make the flash "appear larger".
However, there are 2 things that keep me from the techniques mentioned above. First, at Disney World, I'm always on the go, so I might not have a nice white-colored wall near me to bounce my flash. Or, I may use flash outdoors, where there are no walls. Or, if I use my flash indoors, you know how colorful the walls are at Disney World, so if I try to bounce my flash off those walls, my subject will end up being that same color reflected off the wall.
The second thing is trying to balance between how large a flash modifier I'm willing to bring vs. portability & convenience vs. looking like an idiot
. The Sto-fen Omni Bounce is small enough and discreet enough that I don't get curious stares or comments from others or cast members. Certainly, I'd love to carry a mini-softbox, like the one boBQuincy shows, and I don't doubt that it softens the light tremendously. But in a fast-paced photography situation, that's just 1 more bulky item for me to take extra time to assemble / disassemble whenever I take my flash on / off the camera.
I think the reason the Sto-fen Omni Bounce works for me is because it (1) reduces the light output from the flash by a little bit, (2) it spreads some of the light around the room, if I'm indoors, and (3) it's extremely portable. I've had pretty good luck with it. I'll admit that sometimes I'll notice harsh shadows, but oftentimes, I don't.
As with everything in photography, even the choice of portable flash modifiers is fraught with compromises. Good luck!
Yay! My 800th post!