The Dragons Gate Campaign might work well for you. Our sessions are almost entirely stand alone sessions (one-shots) but they happen within the context of a living world with many other adventures and world/region plots happening around you.  Even though sessions are stand alone they often allow you to effect the world around you in meaningful ways that become a part of the world and future adventures.  We're a persistent world Pathfinder group currently in beta with six GMs and roughly thirty player characters in the world. We've had at least one game every day for the past few weeks. We're just about to push for our last batch of pre-launch players so its a good time to join us. You can check out the campaign information here:  <a href="http://dragonsgate.boards.net/" rel="nofollow">http://dragonsgate.boards.net/</a>   Best of Luck! Gryphyx