Idioms and Expressions with "lassen"

blau anlaufen lassen
to temper (metal)

sich blicken lassen
to show one's face

einen lassen
to cut one, let one rip (vulgar)

die Kirche im Dorf lassen
to not get carried away, not over-do it ("leave the church in the village")

jdn im Stich lassen
to leave sb holding the bag, leave sb in the lurch

keine grauen Haare darüber wachsen lassen
to not lose any sleep over sth

kein gutes Haar an jdm/etw lassen

to pick sb/sth apart / to pieces

another posts to "lassen":

An irreplaceable verb "lassen"

Compound verbs based on "lassen"

http://german.about.com/od/vocabulary/a/lassen.htm