This post by Larry over at OF Blog was interesting, and I thought I'd do my own list here. The idea is to list what age you were when you started reading certain books. Some of the below were books read for school, if I can still remember them.
The Railway Stories by the Reverend W. Awdry.
Transformers (comics) by Bob Budiansky and Simon Furman.
The Beano and Dandy (comics) by various writers.
A bit hazy, but lots of Roald Dahl, various children's books and I think I first picked up Pawn of Prophecy by David Eddings and put it down again since I thought it was too boring. I eventually got back to it. I think I picked up Isaac Asimov's juveniles, the Lucky Starr books, around this time as well.
Various Star Trek novels, most notably Enterprise: The First Adventure and the Dreadnaught!/Battlestations! duology.
This Time of Darkness by H.M. Hoover.
2010: Odyssey Two by Arthur C. Clarke.
The Chronicles of Narnia by C.S. Lewis (due to the fine BBC adaption airing in this year).
Most of the Doctor Who novels and novelizations over the next few years, reaching about 150 books in total.
2001: A Space Odyssey by Arthur C. Clarke.
2061: Odyssey Three by Arthur C. Clarke.
The Caves of Steel and The Naked Sun by Isaac Asimov.
Pawn of Prophecy by David Eddings.
The Tripods series by John Christopher.
The ColSec trilogy by Douglas Hill.
The Foundation series by Isaac Asimov.
The Rama Cycle by Arthur C. Clarke and Gentry Lee.
The Crystal Shard by R.A. Salvatore.
The Amtrak Wars by Patrick Tilley.
Childhood's End, The Ghost from the Grand Banks and Imperial Earth by Arthur C. Clarke.
The Discworld series by Terry Pratchett (Books 1-16).
The Shannara books by Terry Brooks (Books 1-7).
Red Mars by Kim Stanley Robinson.
The Mission: Earth series by L. Ron Hubbard, still the worst books I have ever read.
Lord of the Flies by William Golding.
The Lord of the Rings, The Hobbit, The Silmarillion and Unfinished Tales by J.R.R. Tolkien.
Green Mars by Kim Stanley Robinson.
Tigana by Guy Gavriel Kay.
Nightfall by Isaac Asimov and Robert Silverberg.
Startide Rising by David Brin.
Eon by Greg Bear.
Gulliver's Travels by Jonathan Swift.
Macbeth by William Shakespeare.
Magician by Raymond E. Feist.
The Wheel of Time (Books 1-7) by Robert Jordan.
War and Peace by Leo Tolstoy.
I Know Why the Caged Bird Sings by Maya Angelou.
Great Expectations by Charles Dickens.
Blue Mars by Kim Stanley Robinson.
The Lions of Al-Rassan and A Song for Arbonne by Guy Gavriel Kay.
Titus Groan and Gormenghast by Mervyn Peake.
The Book of the New Sun by Gene Wolfe.
The Reality Dysfunction by Peter F. Hamilton.
Hawkwood's Voyage by Paul Kearney.
King's Dragon by Kate Elliott.
Nineteen Eighty-Four by George Orwell.
Seventeen is when I really got into SF&F in a big way, and tracking the books I read after that point becomes very difficult.
Interesting. Lots I've forgotten or left off, naturally, but it's notable that it was comics and TV tie-ins that first got me into reading on a regular basis (I picked up 2010, my first adult SF novel, after seeing the movie).