Behind the head Lat Pulldown Curls
I love using cables for bicep work. The constant tension on the muscle let's you reach muscular failure more efficiently.
Sometimes you'll be in a gym that doesn't have a Cable cross over, but it will have a Lat Pulldown. This is making lemonade out of lemons.
Keep your elbows tight, your hands right above your shoulders. The weight will need to be light enough for you to pull the bar diagonally. Don't crunch up your body too much trying to ego lift!