Can I Advance an Unrezzed Ice in Netrunner?
Yes, unless otherwise noted on the card text.
I couldn't find this specifically addressed in the FAQ, but it's pretty easy to reason out the answer if you look at all the Ice that can be advanced. For example, several cards have something like this:


  Tyrant can be advanced only while rezzed


This implies that the others can be advanced while unrezzed. To really drive the point home, Wormhole says: 


  Wormhole can be advanced and its rez cost is lowered by 3 for each
  advancement token on it.