You can try listening V-Music. Their technique is quiet good and you can see picturesque Vietnam through their music video. For instance MV Xinh tươi Việt Nam (Beautiful Vietnam)

http://www.youtube.com/watch?v=OhIM1wqZvnc

Have fun!

There are not many boy bands in Vietnam, most of them are rock bands. I can suggest The Men and V.Music, Artista, H.A.T, M4U.. and The Wall (bức tường), a famous rockband.