No shortage o material here. Golly. ..I'd also recommend:
1. Free Saturday afternoon Korean class at Sukmyeong Univ. ( I assume they still have this...start time used to be 2pm)
2. If your feet are already wetted then the TOPIK test prep books and old tests located on their site
http://www.topik.go.kr/ are very useful for practice resources (no explanations though) even if you don't intend to take any of the tests.
3. If your feet are completely soaked and you can't stop studying Korean no matter how hard you try: Korean Grammar for International Learners. A great resource for grammar. There is an exercise book as well.