The Reading Rainbow Connection
Contact Harvest is interesting among the Halo books as it's the first where there are no Spartans involved. They don't even get mentioned at all. It makes sense, since the book takes place before they received their augmentations and went on any actual missions. There's lots of Sergeant Johnson though, and some other characters from Halo 2 and 3 as well. The books really give a lot of insight into the Covenant, especially the relationships between the Prophets, Elites, and Brutes.
The Cole Protocol does have some Spartans in it - the mysterious Gray Team who is mentioned in The Fall of Reach as being too far away to contact/recall. It also features Lieutenant Jacob Keyes and helps fill in the gaps of his life between helping Halsey collect the Spartan candidates and the inception of the 'Keyes Loop' maneuver. There's a lot of different factions in this one, all working together and stabbing each other in the back at different times. It makes for some interesting twists.
Looking at my calendar, I've got six weeks to go until release and five books to read, so I'm feeling pretty confident about making this. Setting goals FTW!