When I was in the library on Saturday, I came across a copy of Halo: First Strike by Eric Nylund.
I figured that since I had spent a ton of time playing the game, it would be worth it to spend a little time reading a Halo book. I didn't expect much - book adaptations from other media tend to be pretty bad.
Surprisingly, the book is pretty good. Nyland's writing isn't up to the standards of the Davids (Drake and Weber), but it's quite readable.
I also discovered something I didn't expect. Though I'd never thought about the Halo backstory very much, I was quite interested in it once I started reading the story. Since it covers the time between the destruction of Halo and the time when the covenant reaches Earth, it's a good way to get primed for Halo 2.