If you like the idea behind PPLNS but dislike the high share-variance inherent to using a small value of N then perhaps consider trying a pool with using the double-geometric method such as eclipsemc.com or yourbtc.net. Both of these pools have merged mining and 0% fee.
From the eclipsemc.com FAQ: "We are currently employing a modified proportional system with a score based system coming online very shortly." They don't say how that proportional system is modified. And then score-based looks just like Slush.
From the yourbtc.net FAQ: they explain that the value per share decreases progressively over time. That's just like Slush, except that the decay is over a set number of shares instead of a random one. What I like with PPLNS is that shares don't decay, they either count at their full value or don't count at all if we're past N.