My husband has a great external flash for his Canon SLR camera. It is the Speedlite 580EX.
This flash mounts securely on top of his camera and works very efficiently. He can take great photos in poor lighting with this flash as it is very powerful. It comes in a nylon padded case and is very easy to store in a camera bag when not in use. This is Canon's top of the line flash, and my husband would not be without it. I have seen for myself photos he took without the flash and then with it, and it is amazing what a difference the flash makes. My husband and I take professional photos at weddings, and sometimes the lighting in churches and reception halls will be very poor. But with this flash, it is not a worry because the flash is powerful enough to light up the darkest area and produce a great photo.
Some of the features of the 580EX External Flash are: flash exposure bracketing (FEB), flash exposure lock, flash exposure compensation, high speed sync, and bounce flash, which will allow you to bounce the flash off of walls or ceilings to get just the right amount of lighting for reducing shadows.
The flash operates on four AA batteries. There are so many great features to it, and with this flash you can be assured you will get great photos. It is definitely worth the price.