Ude Garami (arm entanglement) is a good option.
Check out: http://www.judoinfo.com/quiz0297_2.htm
From the ground, you will find that it is better (i.e., hurts more) when your opponent's arm is in a (roughly) 90-degree angle and the hand is in line with the shoulder. If the hand is too high (i.e., near or above the head), the technique will be less effective.
The drawing at the bottom of the above link illustrates this point.