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 been searching 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 (a) bachelor degree, (b) master degree, and (c) 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].
I think you will be hard-pressed to find actual statement of purpose on the Internet. The one submitted to the departments are destroyed after the application process because of obvious privacy issues. Generally the applicants do not publish their own statements for several reasons. Your best bet is to ask some people you know that might have written one and can send it to you.

Another option is to have a professor or a postdoc help you with your draft because they have probably been in committees routing through these statements and will have a good idea if you are heading in the right direction. There are many ways to write a good statement, you should be able to write a statement from the general guidelines that you can find in the other  answers on this website. After all the statement is meant to test your capacity of developing your ideas and your writing style.