BEND OVAH, BITCH!
Just kidding. But not really.
Other than toe touches, I like this: Stand facing a low-ish box, bench, chair, whatever. place one foot on top of object with leg straight. Lean forward at the hips until you feel the stretch in the back of your leg. Hold 10-15 seconds, then straighten without moving your foot. Rotate foot out, then bend forward again. 10-15s. Straighten, rotate foot in, bend forward again, 10-15s. Repeat with other leg. Sometimes I go through both legs twice.
Don't push the stretch too hard. The other thing you can do with this, and lots of other stretches, is to do it really light -- just until you start to feel resistance but before it's at all uncomfortable -- and hold for at least a minute. "Microstretching." I'm going to do some today, actually.
At the end of the day, your flexibility is going to be limited by your genes, and it doesn't matter past a certain point. I can place my hands flat on the ground with my legs straight but fuck if it helps me do anything athletic.
Also, foam roller.