You can appeal an appraisal if you can prove there were errors. But it is tough. FHA appraisals also stay on file for 6 months so if you aren't successful you are stuck with that value. It's tough on everyone in a declining market but if you have valid issues to raise you might be able to fight this.
With an FHA Loan you can participate in an FHA Streamline Refinance. The best thing about a streamline is that you dont need an appraisal, you dont need to verify your income and there are no cost to you. Let me know if you would like me to help you with this.
If it is something like this, find a bank that will finance you. And, oh, by the way, the best time to get your home appraised is Aug, Sept, Oct. This is because in my area, sales are seasonal and each year their is a bell shaped curve with the highest sales prices in the summer months. this means the appraiser will be using the sales that closed three months ago to determine your home value and they just might be the highest sales for the year.