If you have emptied the trash, your prospects are not good. DataRescueX is the best program to recover files, but they specifically disclaim the ability to recover files that have been emptied from the trash. The longer you leave your machine on or use it, the lower your chances get, because the OSX will overwrite the sectors much more quickly than OS9 or Windows do.
If it is really important data, shut your machine down until you can get Data Rescue X and run it. If it is end of the world important, get prepared to spend $1000 - $4000 at Total Recall or ActionFront for professional recovery services.