If the data is important you can get a quote for a professional data recovery service. This is expensive and can cost from $800 and up. DriveSavers is one of the better services.
Other options is to try Minitools. It may have a different recovery algorithm that may recover more files. Also you can try PhotoRec. It has an option to recover files by file extension. Only pick one file extension you know on the drive in the File Options of PhotoRec. Do not use Qphotorec as this is not as powerful.
The last option I would use if the above two option do not work and a recovery service is out of your budget is chkdsk. It can make recovery of data harder if it fails and that is why I recommend it as a last option.
chkdsk X: /r Where X is the drive letter of your external drive.