Good source for pre PhD level papers/dissertations in Mathematics
Your best source of such information would be to look for electronic repositories that are at least partially "open." The openThesis repository offers one such source, and you might find some information on sites like academia.edu. 

An alternate source would be to look at individual school's repositories. For instance, MIT's DSpace offers copies of many recent MIT thesis and dissertations, which can be previewed by anyone, although you need to be a member of the MIT community in order to be able to download and print documents from the site.