Indeed there are. To be honest, you don't desperately need one, but if you're having problems with white balance and so on, it really makes things easy. Plus they throw out more even light. You can also get very powerful ones, but it's up to you to figure out if your el-cheapo light can give the bulb enough power without burning your house down, I take no responsibility.
Ben, that S3IS has white balance calibration on it. All you have to do is take a picture of a white sheet of paper under the lighting you want to use, and it will set the white balance for that environment.