Your should have recieved an appeal form with your assessment. Did you file for an appeal? You may have missed the deadline. Call the tax assessment office and find out now. Ask them to send you a copy of the "field sales report". They do not do appraisals. They take the value of homes in the area and do an average.
They specifically told me to call them or file for a personal hearing. Do NOT try to negotiate by mail. They may not interpret your information in the same manner as it is intended.
Regardless of your appeal decision, make sure you apply for the Homestead Tax Credit which could potentially ease you into those higher property tax payments. 2007 state legislation that requires primary residence owners to apply in order to receive the credit in the future (or even to continue receiving it.) went into effect the first of the year. If you didn't receive the application with your tax assessment letter you may download it from the link below. Good luck.
You can also have a Realtor do the work for you. I've instructed my agents to notify all of their contacts that they will provide this service for free. Hopefully, you won't have any trouble finding someone to do the same.
One warning - here we have a deadline for filing an appeal. Make sure, if that's the case in your area, you submit before the deadline.
Hopefully, your home really is worth the tax value!