When I first signed up here I posted a question about the monotone class theorem that was closed. Is there a way to find it or is it gone?
By searching for user:me closed:1 you can find all your closed questions. To find more about various similar options, have a look at advanced search tips. Of course, you can add other keywords or search options if you need to restrict the number of results.
It is possible to find your own deleted posts by searching for deleted:1, but it only works for 10k+ users. For more details, see: http://meta.math.stackexchange.com/questions/13948/is-there-any-way-to-see-my-deleted-questions-or-answers