Question:
Does anyone have any references to yoga exercises specifically for people with lower-back problems?

Answer:

Mary Pullig Schatz MD litterally wrote the book on this subject, it's called; BACK CARE BASICS- A Doctor's Gentle Yoga.In general, all the backward bending poses, e.g., Shalabhasana (Locust), Bhujangasana (Cobra) and Dhanurasana (Bow) are considered excellent for lower back problems. Similarly, backward bending poses in standing position are also helpful. However, do these asanas only if they don't give you any more pain than you already have.

I do yoga, and have back pain. The poses that I find the most helpful are the cobra, locust, child pose... any of the back bending poses, I stay away from, because they can upset my injury. If I back bend at all, I make sure it is just the upper back. Also, to warm up in the morning, I do something that could be called the "cat stretch" and also "table" pose. The cobra and the locust ARE backbending poses and usually contraindicated for those w/ back pain. Apanasana (knee to chest) and chakravakasana (sunbird) vinyasa version are two common intial poses (done gently and dynamically) for those with lower back pain. Actually, this can't be diagnoses, much less prescribed via email. Back Care Basics is a useful book, indeed the only yoga book per se on back care but certainly not the only yoga approach. Viniyoga teachers are often back care specialists, but relatively hard to find.