a really good static stretch for hip flexors is called the pigeon pose in yoga. Sit indian style, then leave one leg bent in front of you and take the other leg and put it straight behind you with your kneecap touching the floor.
once you're in this position lean forward and try to put your chin on the ground. this will serisouly stretch your hips and glutes. once this gets easy, reach back straight over your head and grab your foot
like this: http://www.yogajournal.com/poses/863_1.cfm
lean forward in the above pose to get a good stretch on the hip flexor of the leg behind you.