How to recover deleted files in Mac OS X?

The software in the squidoo page that @tj111 recommended needs money to pay for the last recovery step. See this blog article for truly free Mac data recovery programs.

• Time Machine
• TestDisk
• PhotoRec
• Exif Untrasher

There's a nice guide here-- that walks you through the steps of recovering "deleted" files in OS X (using freeware).

Keep in mind that until you recover the files in question, you want to minimize writes to the disk as they can potentially overwrite the deleted files.