This is the most over looked areas on our bikes, and a lot of the times it shows on a lot of our rides involving flat tires. As far as I'm concerned, you get what you pay for when buying them. I ride Continental Grand Prix 4000. Last year, I managed to put 2,300 miles on a rear tire, before changing it out. These have a Kevlar protection that seems to help prevent glass and other objects you might run over. Their price has gone up a little from last year, and now sell for about 55 bucks. There are also other brands on the market, and all the top of the line tires are in the 45-55 dollar range.
Inspect them often, and if you see something that looks like it might be a shard of glass, dig it out. An awl works great. Another thing you can do so your ride doesn't leave you stranded for 10-15 minutes is, always wipe off your tires with your hand when going over, or even close to glass in the road. It takes 5 whole seconds, and all your riding buddies will be happy you did. Wiping the tires off with your fingers takes a little practice, especially the rear. Be careful that your hand doesn't get caught between your tire, and the seat tube. Once you have practiced this a few times, you will be doing it like the Pros.