Before you toss the old ones in the trash, consider recycling them instead! (You can always donate an old pair, but let's face it: if you don't no longer want them, it's a good bet no one else will either.)
Nike's Reuse-A-Shoe Program lets you drop old sneaks of any brand at certain Nike stores (here in L.A., the Niketown on Wilshire is a drop off location) and they'll grind em up and make something new out of them. It's a closed loop system where you use your shoes for playing and then send them on to be recreated into a playing surface like a playground or basketball court for kids. Pretty cool right?