Secret Love Affair - Woman in loveless marriage falls for younger man. It's a drama about forbidden passion, dreams and music, but also about complicated family, friendship and business relationships.
http://mydramalist.com/8929-secret-love-affair It's a good one.
Valid Love - Happily married couple, the woman falls madly in love with another man. The focus of the story is how torn she is between the two men, the heartache of all the characters, the husband's pain and love for his wife and how they all try to figure out what to do. There are also supporting characters who are not too much in the way of the main plot. I liked this drama. I found it hilarious at times, sometimes painfully emotionally intense. Personally I found parts of it a bit annoying and draggy towards the end, but I like the way things were resolved.
http://mydramalist.com/10874-valid-love Hirugao - The two female main characters live in loveless marriages. One is a rich "trophy wife" who cheats on her husband to get some excitement in her boring live, knowing that her husband doesn't love her anyway. The other is a part-time working housewife who is hurt by the fact that her husband is not interested in her as a woman anymore. The two women become friends and things start to happen. The rich wife starts and affair with a brooding artist, and the other one falls for a biology teacher who finds that his relationship with his wife isn't going so well. I LOVED the first half or so. The opinions of the ending differ; I don't know what you like, but you might enjoy this drama.
http://mydramalist.com/10447-hirugao Sayonara Watashi - The focus of this drama is the friendship between the two female main characters, who swap bodies in the first episode... One of the characters is married, and he finds out that her husband is having an affair with the friend. I found this to be a pretty interesting and unusual love triangle, especially with the way it ended. :)
http://mydramalist.com/11368-sayonara-watashi Mitsu no Aji - The main characher falls in love with her father's younger half brother, a doctor who gets married to a co-worker. A lot of people hate this drama but personally I enjoyed it a lot despite the incest theme.
http://mydramalist.com/3006-mitsu-no-ajia-taste-of... (Kanno Miho is great in this drama by the way.)
Koi - The main character falls in love with a literature professor and his wife, who has many lovers and her husband is aware of it. It's a "special" so it's more like a movie than a drama, but still. Loved it.
http://mydramalist.com/8320-koi
