Primetime Adventures (PTA) is a pretty good one. Here's how it generates story.
1. You come up with, as a group, the "pitch" for your TV series. This creates buy-in for the players and gives the choices in the next step some meaning.
2. You come up with characters (PCs) who are protagonists with Issues. They are protagonists because their actions drive the story. The story is focused on the PC's Issue. Some examples (from the book) are Atonement, Control-Obsession, Commitment Phobia, etc. The Issue defines the protagonist and determines what the character's story is going to be about.
3. You set up a story arc for each PC by assigning a number (Screen Presence) for each session. 1 means you're more of a supporting character, 2 builds on your Issue, and 3 means it's your spotlight episode - when your Issue is brought into stark focus and the episode is all about you. At this point you don't know what's going to happen, but you have an idea about how things are going to ebb and flow.
4. When you start playing, each player gets a chance to set the bare-bones of the scene. The player says where it's happening, the focus of the scene (plot or issue), and the agenda of the scene, in general. The GM then fleshes all that out, adding meat to the skeleton. This allows players to drive the story but it still allows the GM a lot of input.
5. When there's a conflict in the scene, the player has resources they can spend to see if the PC gets what he wants. Generally speaking, the more the other players are invested in your character, the more likely you are to succeed. It means that you are rewarded for "good play" - interesting scenes about your character's Issue.
6. In addition to seeing which character gets what they want, which player gets to narrate the outcome of a conflict is randomized. This means that no single person can control the flow of the story; it's all going to be a surprise to see how it turns out. And once again, rewards for "good play" kick in.
7. I think there's something about the reward system that tends to have the action in any particular episode escalate over the course of the session. You start off with few resources and little adversity, and as the adversity builds so do the resources available to the PCs.
What happens is that you have an interesting premise for a series; you bring in interesting characters with issues they need to resolve; those issues are resolved over the course of the campaign; no single person can control the outcome, which is always doubt; as you play out each scene in the game, whatever the group considers "good play" is reinforced by the group.