Please, post really 800 level problem. I've just started my GMAT course and would like to see something from the very top; something so difficult, that will make me crap my pants.
Use the GMATFix Solutions Engine to find your problems. In searching you can set question type (PS, DS, RC, CR or SC), topic (Geometry, Pronouns...), and difficulty (up to 700+). All the questions found will be from GMATPrep. The search page is here
To get you started, why don't you give this little guy a try?
-Patrick
