I discovered PT back in 2009 after reading an article about Gavin Harrison in Modern Drummer. Fear of a Blank Planet was the first album of theirs I bought, quickly followed by Deadwing and In Absentia within a span of about 3 days. Porcupine Tree (as well as Steven Wilson's solo work) has since become my favorite artist.
Here are a few favorites to check out (aside from FOABP, which you already know).
Off the DEADWING album:
- Shallow
- Lazarus
- Halo
- Arriving Somewhere But Not Here
- The Start of Something Beautiful
From IN ABSENTIA:
- Blackest Eyes
- Trains
- The Sound of Muzak
- 0.3
From THE INCIDENT:
- Occam's Razor/The Blind House
- Time Flies
- Octane Twisted
- I Drive the Hearse
- Bonnie the Cat
That last one, Bonnie the Cat, is a particular favorite of mine. Here's Gavin performing it, with a brief explanation of his groove: