EXCUSE ME?! Being flexibe and being strong dont go together? Manuva are you out of your freaking mind!?
Ever been to the gym? Probably not. Yes stretching improves flexibility, but so does strength training. Dont write random bull**** on the threads just because it makes "sense". Shows what you know.
As for the poster's question. The exercise you are looking for is deadlifts. Deadlifts work the hips, lower back, upper back, erectors, hams, calves (a little), quads, etc. Its almost a full body exercise. And yes it improves flexibility alot. It also helps if you do stretching AFTER the workout. Listen to Warboss he knows his ****.