Centered around the Murray Hill L.I.R.R. station, there exists somewhat of a "Korean BBQ Square" with restaurants lining the underground station on all sides. The most crowded of these always seems to be Mapo, although none of the others are ever empty. Some are darker, look more quiet, more intimate.
But do not worry about the 30 minute minimum wait during dinner, the friendly staff will eventually take good care of you, and the BBQ is about the best in NYC. The quiet streets of Murray Hill, Flushing's Koreatown are worth a good wander while you wait anyways.