The Rubik's Cube
I became hooked on the Rubik's Cube during an extreme case of ennui in the July 2005, I had two of these puzzles, incomplete, sitting by my bed and I decided to solve them that afternoon. After briefly looking up a solution online and printing it, I spent the next four hours trying to solve cube with the instructions I had. In the end I solved it and I have been hooked since then.
I'm still speedsolving today, below are various categories to help beginner and and intermediate speedcubers.