If you experience one of those oh-my-lord moments when your back gives out on you, know the first line of action: Grab the ice. Applying ice for 20 minutes at a time is going to lower the inflammation that's occurring from the strain. After you remove the ice, the blood flow increases in a way that relieves injured tissues away yet doesn't promote inflammation. Use ice for the first 24 to 48 hours, then switch to heat, which will help promote blood flow to speed healing (be it though pads, sauna, wraps, heating pads, fire-breathing dragons). By the way, when you use ice, your back will feel better afterward as it works to warm itself up. When you use heat, it feels better during the heat treatment itself, and then tends to stiffen up when you stop using it as the area cools down. Only use heat for 20 minutes at a time, or else you can overheat the muscles.
Of course, you can also use anti-inflammatory drugs like ibuprofen to reduce pain and inflammation, and docs may prescribe a muscle relaxant or shoot local anesthetic into the muscle (trigger point injections) to keep the darn things from spasming and feeling tighter than a cyclist's shorts. For a natural alternative, willow bark, the herb from which aspirin was derived, is often as effective as ibuprofen, and does not carry the risk of irritating your stomach if you rub it on.
You can also try certain stretches and exercises to alleviate back pain.