USB flash recovery tools?

[Jon Pruente]

I've got a 512MB USB flash keychain.  Tonight I tried to use it and it
didn't work.  Ack!  So, after some cleaning of contacts and messing
around I got it to be recognized on my Mac mini, but with no
filesystem.  I dd'd the contents to a .iso file so I'd at least have
some sort of backup.  As it stands, the backup file is smaller than it
should be (480MB?) so I'm not too confident in it.  Anyway, can anyoe
suggest a recovery tool for the drive itself, or to process a block
dump?  Either Mac OS or Linux tools would be good.  I'm fairly sure it
was in FAT32.  So far Googling tends to bring up demos and trial ware.