There are suggestions that the 5S will have faster processing. And they are implementing a biometric fingerprint scanner. This new feature will be used to confirm the identity of the owner.
The 5C will be an entry-level iPhone, jokingly the C stands for Cheaper. It will have a plastic shell and the same processing power of an iPhone 5. As they are using plastic, the 5C will sport a variety of neon colors (such as yellow, red, green, blue, and white). There 5S will have new colors as well (grey, silver, and gold).