I find pigeon pose to help loosen up my hips too: http://yoga.about.com/od/yogaposes/a/pigeon.htm. If I slowly drop my head to the floor in front of my knee and relax into the stretch, it's pretty intense-to-uncomfortable.
I sure do like this one!
Doin' the Pigeon,
Doin' the Pigeon,
people may smile but I don't mind,
they'll never understand the kind of fun I find...