[draken]
What are you looking to strech out? The traditional keeping your legs straight, feet together, and touching the floor works.
There's also splits, but I find one foot-streching (reaching for one foot, while one leg is tucked in) to work better for me.


Static stretches are good means to safely loosen the joints (effective only after warming up the limbs first though) but are not the most effective means of improving one's flexibility. The most effective static stretches are PNF stretches done after a workout when the muscles are exhausted.

[draken]

If you're working on kicks, try leaning against a wall with one hand, having your base-foot turned to the proper angle, and holding out your leg in the CORRECT position for long periods of time. You can slowly increase your height. This will help your flexibility as well as your kicks.
And practice deep, correct stances.
If you want to go the extra mile, try taking some gymnastics classes.


There are different types of flexibility a martial artist has to consider. These types of stretches (active flexibility) are great if you're a wushu martial artists or all demo/kata artist and want to be able to stick your leg up in the air impressively. They are not however effective means to improve your flexibility if you're a sport or competitive sparring martial artist and need flexibility and speed/power. Usually, the reason martial artist see increases in their flexibility over time (and height in their kicks) is because of the routine of actually kicking during classes stretches the leg, these "dynamic" stretches in general contribute more to increased flexibility than static stretches.