I first read this when I was in college - my mom gave me the first book for my birthday, and I blazed through it and then made us stop at Barnes & Noble to get books 2 and 3 in the middle of a family road trip, and I remember book 4 came out shortly afterward - so 2000, then. I've read it at least once since then. This one's always been a particular favorite of mine in the series.
-----
Reread January 2016: I'm noticing a few things on this reread through the series. One is that the characters who went to school with Harry's parents are about my age now, including Sirius and Remus and Snape. Realizing this gives this reading an interesting flavor (as Snape seemed ancient when I first read the book, but he really can't be more than 40 and is probably closer to 35). This reading is also very inflected with knowing what happened in the past (which Harry is just finding out) and what will happen in the future. Just seeing how events unfold is really interesting and how each book sets Harry up for the challenge he'll face in the next.
-----
Reread January 2016: I'm noticing a few things on this reread through the series. One is that the characters who went to school with Harry's parents are about my age now, including Sirius and Remus and Snape. Realizing this gives this reading an interesting flavor (as Snape seemed ancient when I first read the book, but he really can't be more than 40 and is probably closer to 35). This reading is also very inflected with knowing what happened in the past (which Harry is just finding out) and what will happen in the future. Just seeing how events unfold is really interesting and how each book sets Harry up for the challenge he'll face in the next.