I use Anki (http://ankisrs.net/).

The app store version is $25, but the desktop version is free. There's also a free web app that can be used from handheld devices with internet access and a free Android app. You can sync across multiple devices via the web app.

The iPhone version has drastically increased my use of Anki.

I do most of my Anki revision through my iPhone: I can use it anytime I have 30 seconds to spare. Such as waiting for the dentist, waiting at a pedestrian crossing, waiting for breakfast to cook, waiting in line for lunch... etc.

I'm a very patient person as I'm extremely happy to wait for things now :)

I have used Supermemo for five years and learned thousands of Japanese words, and now I'm working through Chinese. Use whatever program you want (Anki, Mnemosyne, Supermemo, etc.), but stick with whatever you are doing, and use SRS to save your progress.