I LOVE using sun salutation as a warm up. I know that some yoga purists might not be so keen as using the sequence as a warm up, but it works well for me. It stretches hamstrings, hip flexors, upper and lower back, shoulders, ankles and wrists, etc. And it's all dynamic stretching, so it doesn't hurt your lifting numbers for resistance work.
Just Google 'Sun Salutation' and loads of videos and step-by-steps come up; I'll usually do two (each side!) slow to start off with, and then a third on either side to get my heart rate up a bit.
If you need clarification, just ask;
ps. Something else that might be helpful is a foam roller, which (when used properly) can help work out stiffness and generally increase mobility and reduce pain. Tennis balls or even a rolled up blanket can work, if you don't want to buy anything new right now.