I found no useful personal statement samples when I was searching for ideas for writing mine. I ended up just writing about what I liked about my research experiences, course work, etc., and made a point of not wasting space repeating things that can be found elsewhere on the application (e.g. numbers like GPA, receiving awards [put it on your resume or CV, if included], etc.), and never mentioning something in the SOP without a purpose. For example, don't say "I took class X and got grade Y." That's visible on your transcript already. If you really want to emphasize that you took this class, you could instead say something about how, when you took class X, you <learned this interesting fact, really enjoyed it for this reason, it is impacting your grad school decision because of ...> etc.
Don't go for the cliche childhood story. Be concise, the adcomm has a lot of these to read and will appreciate brevity (but still say what you want to say).
Finally, be sure to edit it a lot and have many people read it. Make sure it is grammatically correct and flows well. Based on many samples I've seen, that's enough to make it stand out.