These are the two websites where I learned a lot of natural expressions and vocabulary.
http://www.koreanclass101.com [ For this site, you have to sign up for free, then you have access to tons of free lessons and videos. I used this site for about a year regularly, just listening to a lesson 3 or 4 times, taking notes, practicing, etc. There is also the option to become a "Premium Member" by paying... which I haven't done ;) ]
http://www.talktomeinkorean.com [ This site is amazing, lots of videos, cute conversations, creative lessons, active comment replies, and a great chance to really improve your Korean with personalized lessons. Just check it out!! ]