I have always tended to get back pain if I don't work at it. I've searched online and you can find lists of exercises, or videos of how to do them. I have a few books but my current fave is this one: 7 weeks to 300 sit ups. Despite the title, its got about 30 different ab/back exercises, with specific plans based on your current level. A nice variety, and I like just having to look at a list, and not have to decide which to do for the day. I've tried yoga, I never stick with it because I find it boring -- personal preference I guess, but it probably works too.