Try running an undelete application. I've had good luck in the past with the one from "Norton Utilities," but it's been years since I've used it. I assume they still make one.
I know someone who swears by "File Salvage," which is a program Apple recommends and sells here:http://www.apple.com/downloads/macosx/system_disk_utilities/filesalvage.html
Either way, you'll want to run the software as soon as possible after deleting the application, otherwise you risk overwriting the data in question.