I'm currently going with 65psi in front, 75 in back, based on http://sheldonbrown.com/tires.html#pressure (I estimate me + bike is around 85-90kg, making this table pretty much bang on for me, but ymmv). I have Marathons, I think they're rated to 95; at that pressure I'm bouncing around everywhere though (awful pavement around here). I think I'll probably stick with the 65/75 setup cause it seems to be working out well.