Your pedagogical approach sounds suspiciously like the one in many Math Circles. The National Association of Math Circles has problem lists on their [website][1]. Here's [another problem set][2] which looks interesting.  

If your intention is to leave these students with the sense that there is fabulous ongoing research in mathematics, I'd recommend the [Five Golden Rules: Great 20-Century Mathematics and Why They Matter.][3]  It's quite accessible because it focuses on the general ideas.


  [1]: http://www.mathcircles.org/
  [2]: vhttp://www.sfmathcircle.org/sfmc-sampler-probs.pdf
  [3]: http://www.amazon.com/Five-Golden-Rules-20th-Century-Mathematics/dp/0471193372