Labor of love
When you love to do something from your heart.

Lame duck
Very ineffectieve products/ business

Land of nod
Very sleepy.

Landslide victory
A big win, usually use with political election.

Larger than life
Unique, much better than normal

Last laugh
If you have the last laugh, you win at last.

Last legs
Exhausted

Late in the day
Too late to change/ adjust

Laugh a minute
Very funny

Lay by
Save something for future use

Lay down the law
Tell people to do something exactly and instructively.

Lay off
Terminate the employment

Leave someone's high and dry
Leave someone completely alone

Lemon
Defective

Left in the dark
Really don't know what to do. Not given a any information.

Left handed compliment
Unsincere compliment

Let the cat out of the bag    
Accidentally expose the secret

Live from hand to mouth
Live with only little money. Just enough to survive

Long in the tooth
Too old to perform work

Lose the head
Can not control the temper anymore

Lost train of thought
Forgot what you were talking about