Hip flexor stretch (most people have very tight hip flexors, which can contribute to back pain).
Trunk rotation (this is a good, u can also use it as a mobility exercise & also hold the stretch on each side, can often give good relief).
Knee to chest.
Its not really the variety of stretches thats the issue. You just need to choose the right ones & stretch for the right amount of time. (beleive me, having worked in the fitness industry for a fair while, it gets boring giving out the same old stretches). There are many muscles that can contribute to the inner workings of the lower back. If you are a runner specifcally the Quads and Hamstrigs need careful attention. It is also important to stretch the Hip Flexors (top of quads) as if the are tight this can cause tilting of the pelvis. Due to the mechanics of running the Hamstrings tend to increasingly tighten, so these will need to be targetted.
Abdominal Endurance is also a key factor in the avoidence of lower back pain/injuries. This doesnt mean that you should do sh*t loads of Sit-ups. Its more to do with isometric strengthening (holding 1 position) ie, the Plank & slow Crunches. Also attacking different muscles in the abdominals such as the Transverse & Obliques (the sides). Mobility is also key in the fine tuning of the lower back.
This link has some pics of more & also the Mobility section has some good explanations of different types of stretching.
Its also more important to stretch after exercise, there is very little evidence to prove that stretching before a work out/run has any benefit. Ideally one would spend a full session on stretching and mobility... but this is not often practical especially when its hard enough to fit in a full exercise session.