You either sell for the appraised price or pay to have it reappraised.

There is hope. I've seen reappraisals come in at different price points when a different appraiser comes in & pulls a different set of comps.

Jennifer,
Which side has this issue, your house for sale or the one you are buying?

In my experience, most buyers will want to pay no more than what the appraisal came in at or they will terminate and release the contract. The only other solution is to see if they'll allow you to do bring in another appraiser; however, appraisals are all coming in very low right now because ot the whole mortgage situation.
I always advise my clients to provide a list of all the improvements and upgrades that they've done to their home and if possible, I will provide that information to the appraiser BEFORE the appraisal is done so that he/she doesn't miss anything.
Unfortunately, your situation is all too common right now, and your only choice to is lower the price or not sell, because most likely another appraisal will be very simliar to the first....