There are plenty of times when you take your camera out with you, but don't feel the particular need to bring along an external flash — and then you need to find some way of diffusing the flash to make your photos less horrible. Sure, you could jimmy a diffuser out of tissue paper, or use a business card as a simple reflector, but a gadget like the Easy Bounce is at least vaguely more reliable. Available through eBay and a few online stores, the Easy Bounce is a pocket-sized accessory that can be taken anywhere.
The bouncer goes for around $30, and is small, light and comes with a nifty little carrying case, so you can easily throw it in your pocket when you go out shooting. It slides into your camera's hotshoe, and sits directly in front of the pop-up flash, bouncing the light. Yes, you're going to lose a few stops of brightness, but it'll give you a much more diffuse and less harsh shot without the need to bust out any serious hardware.
As always, buying objects like this from eBay and dodgy online stores can mean you don't know how well it's made, but for $30 it's not going to break the bank, and could be a welcome addition to a light-weight shooting kit.