Nobody seems to have mentioned it but you do not want to do anything on the system if you need to recover files. EVERYTHING you do pretty much writes back to the hard drive and you take a risk of overwriting an area that has a file you need back. Shut your system down and get one of the CD's listed and run the recovery to another disk (external) if possible.
The software mentioned are all good, along with Data Rescue II.
You can try Stellar Phoenix Macintosh Data Recovery Software. It recover data after trash bin has been emptied. It supports HFS, HFS+, HFSX and HFS Wrapper file systems.
Download the demo version from: http://www.macintosh-data-recovery.com
Demo scans the drive and shows the preview of the recovered data.
1.) Do _not_ delete things you might still need.
2.) Use an external harddrive bigger than your internal for backup purposes and let Time Machine handle it. (In Leopard. For Tiger and earlier use a 3rd party backup application.)