State laws differ so the fines and penalties for being cited for driving without insurance differ as well. Many states take an uninsured driver pretty seriously. To find out what your specific state laws are and thus the penalties for driving a vehicle without proper insurance, contact your state's Department of Motor Vehicles.
Some states might only find it to be a traffic offense and require you to acquire car insurance. In general though, penalties for being an uninsured motorist can range from a citation with a fine of $150 to $500 or more, the vehicle being impounded, license and/or registration suspension and imprisonment.
For example in Florida the DMV can suspend your driving privilege including your vehicle registration and tag for up to 3 years or until proof of insurance is provided.
In California failing to show proof of car insurance can result in fines of up to $500 plus impounding of the vehicle and suspension of the person's driver's license.
If you were involved in an accident while being uninsured, your state might have harsher penalties, including such things as being required to carry a SR-22 policy for a certain period of time.