Another easy thing (think free!) to do is rotating your tires. I normally rotate mine every 5000 miles and if I let it go too long, I get weird vibrations at different speeds.
I always move my rears to the front on the same side and then, cross the fronts to the back.
Left Rear -------> Left Front
Right Rear -------> Right Front
Right Front -------> Left Rear
Left Front -------> Right Rear