What are effective yoga positions for back pain relief?

Gentle Stretching. Gentle poses that stretch the psoas and quadratus lumborum musculature can often be helpful in treating/preventing low back pain. Positions such as downward dog, cobra and "warrior 1" can help. However, it is best to use these positions as part of a broader yoga routine. I recommend taking a local yoga class to learn how to safely and gently utilize these forms.
Not sure. Yoga positions are not my area of expertise! I have noticed that my patients find pilates more reliably useful vs. Yoga.
Try this! Definitely use pain as your guide, but here are some suggestions: here's some short video advice: http://www.Youtube.Com/watch?V=20zybmbnvou here's a more detailed academic review article: http://www.Intechopen.Com/books/low-back-pain/yoga-as-a-treatment-for-low-back-pain-a-review-of-the-literature.
Hatha Yoga. Hatha yoga focuses on basic chakra - help with body alignments and helps with back pain. There are other types of yoga available - use gentle streches to prevent muscle injury.
Stretch... Last time i looked; sun salute and downward facing dog(i think i spelled it correctly) should be effective in answering your question. The positions depend upon the etiology of the 'pain'.

Related Questions

What are recommended yoga positions for back pain relief?

Experiment. Yoga is a way to stretch. Keeping your "core" (tummy and back muscles) limber and strong can help reduce back pain. Experiment with the movements and positions. Choose those that work the "core." a little discomfort is okay. If a position is really uncomfortable (during or after), try something different. Read more...
Take some classes. Stretches are great for back spasm. Try it you'l like it. Read more...