I'd second Stubacca's experience on slime. In my experience, it makes a mess without any corresponding improvement in flat protection. I'm actually surprised that it doesn't seem to work.

Tuffies help a little, but better quality tires are the only thing that have worked for me here. I'd considered Armadillos, but didn't trust them because I thought they were too light. A lot of people have had good results with them. Others like Continental Top Touring. I've gone about 3,000 flat-free miles on my Schwalbe Marathon Plus.

Paul