Where can I find good examples of personal statements [BSc, MSc, PhD]?

In my country, there is basically no culture of personal statements for university admission. However, now I find myself in the need of writing a convincing one (note: my field is mathematics). I've searched the web for some examples to get to know what an academic personal statement looks like, but unfortunately I couldn't find any good example.

So my question is: could you point out where I can find some well-done personal statements from which I can really see what a good one is like? I would appreciate if you could point out references to personal statements for admission to - bachelor degree - master degree and -PhD [indeed, I have to do mine for a quite peculiar purpose and for this reason I'd prefer to read examples from each of the above categories].