I disagree about "Fly By Night". I find myself listening to this one a lot, but then again these are just opinions. What I did when I first got into Rush was buy Chronicles first (although as Tony said "Moving Pictures" should really come first) and then used that to decide which other stuff I liked (This will give you "La Villa Strangiato", but its not the re-mastered version). Of course I've ended up liking everything, but I didn't know that at the time. Like I said before, Chronicles is not an album you'll end up listening too a lot if you really get into Rush, but it does give an amazing overview. Listening to the first and last songs makes a big impression about how much the group has changed.

All this aside I would say that Moving Pictures should be your first purchase and 2112 should follow in short order (as it's a landmark type of album with great music). Just my own humble "wrong" opinion