Note: This review covers version 1.38.
Undeleters should be portable, since installing a program lowers the chances that you'll successfully recover that lost file. My current favorite free file recovery program is Recuva. It comes from Piriform, the folks who make CCleaner. This is the portable version, suitable for toting on a USB flash drive.
Note: This program is donationware. It is free to try, but the author accepts and encourages donations towards further development.