The ultimate in puncture protection is the Schwalbe marathon plus, though it's rather heavy. The marathon is lighter and still pretty good. Unfortunately neither goes below 25 mm. The Michelin krylion is also quite good - apart from the rear 25 mm I fitted, which punctured 4 times in 1600 miles - I replaced that with a marathon. The front has done 4000+ miles without problem, though. The krylion has now been replaced by the Pro4 Endurance, as PPete says, and is supposed to be "better", whatever that means. The durano plus seems quite good: a few people run it on the FNRttC and they don't seem to have too many issues.