Hip mobility is important for many different reasons but two trends that you will tend to see with a loss of mobility in the hips are:
1. Low back pain
2. Knee pain
For those two reasons alone it should encourage coaches and trainers to put an emphasis on hip mobility in their program design.
Here are a few things we do at IPT:
These are all performed as static stretches except for the first one which is "active" hip internal/external rotation.
1. Hip Internal/External Rotation (first 2 pictures)
2. Wall Splits
3. Rectus Femoris Stretch
4. Quadruped Piriformis Stretch (read this for a detailed explanation)
"ELBOW TO INSTEP MATRIX"
This is one I stole from the guys at T4TG. For those of you familiar with 3D stretching, this offers a nice 3D effect to an already great stretch.
This a one from Mike Boyles "joint by joint" DVD.
"COOK SQUAT 1 AND 2"
The Cook Squat 2 is the progression as raising the arms overhead lengthens the tissue through the body requiring more flexibilty.