Oh man there are a few, mostly all scifi. I have to say recently I've been getting into the Halo lore and I'm so surprised at how rich and full of depth it is. I've played all the main games - the original trilogy, Reach, and 4 - and maybe I just wasn't focusing on the story enough, because I didn't know more than the Master Chief's story pretty much. The universe was seeded for life by the Precursors, who held the Mantle of Responsibility for the galaxy and they created the Forerunners and the humans (ancient humans). The Precursors decided humans would take the mantle instead of the forerunners, and the Forerunners eventually revolted and killed the Precursors. Or they thought they did, because basically the Precursors are space gods and can't really die.

The Precursor's physical remains become a sort of dust which ancient humans discover on a derelict ship or something, and over thousands of years they discover that the dust has a calming effect on their pets (think space dogs). This messes with the space dog's genome and thousands of years after that, some of the space dogs start exhibiting a sickness that mutates them, and this sickness jumps to humans and all other living creatures, and bam that's The Flood.

So the Flood is a mutated form of the Precursors, and the humans start a scorched earth campaign to eliminate The Flood. Big war, lots of people die. The forerunners get pissed because they don't know about The Flood, and think the humans are just attacking and killing planets (some of which are forerunner colonies). So, now the humans are fighting a war on two fronts, with the flood and the forerunners. Yeah the humans lose. The Forerunners de-evolve the remnants of humanity and send them back to earth, and these are the hominids.

Millions of years down the line we re-evolve to the point the ancient humans were at, and then the Master Chief is born. Also the ancient humans had an alliance with the beings who would become the Covenant's prophets, and the prophets betray them at some point. It's all very complicated, and I didn't know any of this from the games and don't have a 100% clear picture of it yet. But it really makes me interested in reading up on the Extended Universe.