Seoul Pub and I don't mix well. I really liked Brixx in Itaewon, on the hill next to KFC, but they changed it from a lounge to a half lounge/half techno dance thing...not nice. Wolfhound is also not bad, but they close early compared to everywhere else.
I really like Hongdae but I think my favorite place is Sinchon. Woodstock in Sinchon is one of my favorite bars ever. It's a shit hole but the music is awesome and the drinks are pretty cheap. I love seeing Koreans go bananas for classic rock.