Tight Hip Flexors

I do what's sometimes called "swans"--lying on my stomach, hands at around shoulder level, push your upper body up while basically leaving your hips on the floor (they can come off a bit). Or get down on bended knee (you know, pretend you're proposing), and lean forward so that the back leg is at a slight angle--you should feel it in the front of hip on the back leg.

The pigeon yoga pose helped me solve this problem. Mine were so tight, it was affecting the way I walked, but I've had very little trouble since I started incorporating this into my post-workout stretches. Hope it helps!

http://www.youtube.com/watch?v=FVlX5HNKamw

Look up yoga "hip openers" on you tube. There are a ton that work well.

If the problem is your iliopsoas it may be helpful to see a massage therapist. Foam rolling and stretching are awesome and you should continue doing both of those regularly, but I've found that getting a massage about every three weeks has really helped keep me in working order with all my running, weight training and activities. Sometimes the muscle attachements are very difficult to get to on your own (iliopsoas is one of those)

To choose a massage therapist I would sort of interview them beforehand, and choosing a random spa may not get you what you're looking for. I would ask them about their background, where they went to school etc. and make sure they know how to work the iliopsoas. Another culprit, strangely enough could actually be your quadratus lumborum or piriformis muscles, the body is really good at compensating for imbalances to keep you in the proper upright position. So I would have them work those muscles as well. If you mention these muscles and they don't know what they are, find someone else! Rather than go to a spa I would reccommend asking around at chiropractor's offices.

Go to YouTube and search hip, glute and hamstring stretches. You'd be AMAZED at how much tightness you can get in the hip area from overly tight hamstrings!!
Good Luck!