This is a difficult challenge! I have many favorites that I had to leave 
off this list because 7 is just such a small number! But here's a list of 
my 7 current favorites, based on what I'm playing the most often right now, 
or would be most likely to be enthusiastic about playing. Of course, being 
rather badly biased, most of these are my own designs, but isn't that what 
you'd expect of me? And to make matters worse, two of these are games I 
haven't even released yet! (Sorry about that...) Anyway, here's my list:
  1) Binary Homeworlds
  2) Secret Project PD-09
  3) Secret Project MB-17 (aka IceGlotz-17)
  4) Zark City
  5) World War 5
  6) Volcano
  7) IceTowers
Honorable Mention: Martian Hold'em and Hearts (i.e. using the pyramids as 
scorekeeping tokens)
More Honorable Mentions: Black ICE, Martian Chess, Treehouse, and RAMbots
As for my 3 least favorites:
  X) Zendo: I realize Zendo is wildly popular with some, but I'm
     never interested in playing. It's just not my kind of game.
  Y) Gnostica: I wrote a whole essay about my beefs with this:
     http://www.wunderland.com/WTS/Andy/Games/IPreferZarcana.html
  Z) Spicklehead: I wish these rules didn't even exist. The idea
     of someone getting hurt by my beloved pyramids is my worst
     nightmare, so the humor of this one is lost on me.
Great question!
-- Andy