Psalm 130 is one of my favorites. So much so that I fear writing anything about it because my words would not do the psalm justice. I will say that I feel like I have been waiting on the Lord quite a bit, and this psalm comes along with the good encouragement that my waiting will not be in vain for He has not marked my iniquities.
anyway, Todd Pepperkorn has an old sermon on this Psalm here. apparently he's hosting a Lenten preaching seminar next winter based on this and other penitential psalms. I'd be curious to know how his dark road experiences might have changed his approach to preaching 130.