Keep stretching the shit out of the ankles - as Allen said, sit in a squat, rest your forearms across one knee at a time and lean on it so you can drive the knee down.
Another trick is to send the knees outside the feet (i.e. instead of the thigh and foot being parallel, the thigh is at a slightly greater angle than the foot away from center). This may get you a few more degrees, especially if you have ankle problems like steven (and me). But soleus inflexibility can feel like joint limitations - trust that stretching will help, but it takes a long time and much stretching througout the day.