Which stretches will help me improve flexibility for kickboxing?

I was recently awarded best answer in Yahoo! Answers by replying to the following question:

Ive recently taken up kickboxing and my kicks lack power mainly due to lack of flexibility. Could anyone give me a stretching plan which i can fit into 10 minutes of the day? Thanks alot!

and here was my answer:

In order to offer a more accurate answer it would be useful to know what kicks lack of power due to flexibility. In any case it’s relatively difficult to explain what exactly doing as it would be necessary the assistance of an instructor that understand what you are trying to do.

Leg flexibility can be improved by consistent repetitive stretching and relaxation exercises that can be done both from standing and from a sitting position. These exercises will help most kicks, and in particular the ones that do not require to open your hips (like front kick, axe, crescent kicks). Splitting your legs and working out the hips and internal abductors will help your side, round and hook kick.
Your approach is right, 10 minutes extra per day will do a great deal if you are consistent. The most important thing is trying to relax your muscles when stretching, release every tension and breath slowly: treat your muscles well and they do the same to you.