Studying Korean is by far the most challenging thing I have ever done so far in my life (I think).

I've been studying since 2012 and interestingly enough fell in love with K-pop because of studying the Korean language after I had already started studying the language xD

These are the resources I have used so far:

1. talktomeinkorean.com --the BEST place for learning Korean. It's completely free and you learn through podcasts. They're actually VERY fun to listen to. They're like listening to a very cool radio talk show that teaches you Korean. It is just AWESOME. I discovered this site through this other website. They charge for their membership, so if you're on a tight budget, I wouldn't recommend it. But still, it's good to know about all different types of resources that are available through the internet.

Anywhoo, back to TTMIK.com (the BEST website ever!): they have 9 levels of Korean lessons (so far) and they're still recording lessons as well as doing some other side projects. If you want to start studying right away, click here. Start with level one lesson one, people. Don't skip any lessons and download the PDFs. They have 25-30 lessons per level...so they're about 300+ lessons or so. It does sound like too many lessons, but trust me when I tell you, you'll come out a lean, mean, Korean language machine after you've listened (AND REVIEWED) all the lessons. I have listened and re-listened all the lessons at least 3 times each lesson from levels 1 through 4 and twice for levels 5 and up. (I'm passionate about the things I do.) Here is their Youtube channel BTW. ^O^

2. Books! I have a few of those:

• TTMIK books. They're pretty similar to the Korean lessons you can find for free on the site, but I have two of the (autographed ^O^ by all the teachers gaah <3) levels at home because I can study on the go and look cool. Hehe. And plus, talktomeinkorean.com offers you FREE language learning...you can't really put monetary value on the amazing efforts these people do to help us waegukins learn Korean... So, if you study with their lessons, you might as well do at least a little bit to help them publish even more content for us :) 
• Once Upon a Time in Korea: an Elementary Reader. This book is awesome. It's basically Korean fairy/folk tales written in an easier form of Korean (along with vocabulary translations) to help us get in tune with our inner Korean. BUT! Even though this is the beginner level, you may want to purchase this book only after you've studied at least 8 months to a year of Korean. You need to be familiar with MANY grammar points to be able to study with this. When I bought this book I had almost a year of hardcore studying so I was kind of ready for the challenge...and it proved to be too difficult for me at first. I had to put the book away  for about two months and then came back to it after I had studied a little bit more. Pros: you'll learn lots of new words and reinforce your reading abilities (such as speed, flow, etc.). Cons: some of the vocabulary is a little bit outdated and honestly kind of old. The language you find in this book is closer to that in historical Joseon era Korean dramas. So if you're trying to be conversational this book might not be for you. I consider myself a thorough learner, though. So I feel the need to study Korea and its history and tales along with the language.
• Cultural Readings from Folk Tales, Legends and History: an Intermediate Reader. Well, the title pretty much says it all. The book's devided into Fairy Tales, Folk Legends and actual Korean history. Through this book you can learn more about Korea and their values and morals that are instilled to children through these stories. And you can also read about how the Korean flag was created as well as the Korean language along with many, MANY other stories/historical facts. I haven't finished reading this book yet. The language is rather challenging for me still. I'm currently giving this book a little breathing time...like wine...I'll go back to it this summer (hopefully). This book is only for the high-intermediate reader.
• Learning Korean Through Korean Fairy Tales. Another awesome book. I recently purchased it and am not through reading it yet...but I really like it so far. It has ALMOST no English at all in it (which can sound intimidating, but it really isn't when you're at the level of learning that I am in). My favorite kind of excercise in the book are these little squares with multiple sentences in them. They give you a word which they use in a sentence as an example and you have to figure out what it means. It actually makes you THINK! Faaaargh so awesome. My favorite blogger and the only blogger I follow posted a review for it. Check it out here.

3.Lang-8.com. This website is a community of people who are really into learning different languages. The way it works is: if you need help with your language skills (it can be any language...seriously, ANY language), you post a journal entry and wait for it to be corrected by a native speaker of your target language. Sounds too easy, right? Well, there's a "catch". You have to correct entries if you expect yours to be corrected promptly. You can search through different journal entries in your native language and help out a fellow language learner. In return, your own journal entry will gain popularity with the site's community and you can get the sweet feedback you're seeking. I've posted a few entries on my journal and I always receieved corrections like...SUPER fast because I was always correcting entries in English and Spanish. Getting journal entry corrections is not very hard when you share your own language skills with other users. (This site doesn't charge you for the basic membership so..what's not to like?!) Here's a link to one of my journal entries. Gah!

4. Talk to me in Korean Iyagi lessons. These are dialogues in 100% Korean spoken slower than Koreans usually do--provided with a full transcipt of the conversation if you need it. You're pretty much going to listen to two or three people talking about a variety of subjects ...all in Korean. So yeah...go ahead and check out their first lesson here and hit a wall like I did and realize you will never EVER learn enough Korean to understand these conversations. Then study all the TTMIK levels and go back to the first iyagi lesson and you will be amazed at how much you will be able to understand. I always thought that when people reach Iyagi lessons levels they're Golden Ticket status in life. Well..I'm not even sure what that Golden Ticket status even means or why I thought that...but one thing's for sure: when you reach this level you can pat yourself on the back. I love these lessons for their lack of English as much as I hated them at the beginning for the very same reason! <3

5. Doki doki postbox. This is an app for meeting people from all over the world...but it's a Korean app so you do get many Koreans who are usually willing to help you practice your Korean skills. SOOOOO many Koreans I've come across while on this app know VERY little English so our conversations are mostly in Korean and if you write something incorrectly or if it's not natural...well, Koreans in general I've found to be very cool people and if you're a foreigner who's learning their language they help you a lot and encourage you to learn more.

So..yeah that's mostly it for my language learning resources....

There you go biasedonaron.

Hope it helped!