Five Times Nathan Petrelli Crashed Down to Earth, by yahtzee63
Yahtzee's fic is always brilliant, but this take on the "5 things" format (spread along Nathan's life from childhood on up) is a subtle, nuanced, very-nearly-canon exploration of Nathan's character. The good, the bad, and the in-between stuff.
Spoilers up through the season finale (and possibly next season--*crosses fingers*).
. . . everything else in his life was abstract. Only Peter was real.