Before You Know It (BYKI) is a program I came across a while back and I really like it. It uses a flashcard system to display Korean words and their English equivalent. The cool thing is that each card also has a picture of the word. It reminds me a little bit of Rosetta Stone except this program is free. You can opt for the pay version in which you will get more words and resources.
There is an iPhone app but unfortunately it doesn't have Korean yet. Maybe they'll get it sometime soon because the app is free and it looks very user friendly.