Since I started cycling regularly, I have noticed that I tend to get tight in a lot of places; hip flexors, hamstrings, lower back, IT band. My hip flexors, however, take the brunt of my stiffness.

I must echo what loni0908k said about yoga and pilates. My gym offers a class called BodyFlow, which is a wonderful combination of Tai Chi, Yoga, and Pilates. I've been doing it for almost two years now and have noticed a significant difference in my flexibility. Since beginning cycling a little over a year ago, I have noticed that if I do *not* do BodyFlow on a regular basis, my hip flexors (and other body parts mentioned above) suffer the consequences. I'm definitely a firm believer in stretching and flexibility training. To me, it makes a WORLD of difference in everything I do.