If you haven't shot new photos on the SD card yet you can probably still recover them. The key is don't use the SD card at this point for anything other then running recovery.
Personally I've had good luck with the Rescue Pro package that comes free with Sandisk Extreme CF cards.
http://www.lc-tech.com/software/rprodetail.html
I know many photographers who swear by PhotoRescue which has a free demo that will show you whether it can recover your images before you have to buy it.
http://www.datarescue.com/photorescue/
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