You have two obvious choices: either buy a new speaker or replace the entire driver assembly. The hidden option number three is to repair the speaker yourself. As long as the paper cone isn't damaged then really all you have to do is replace the foam and gaskets around the paper cone. This could save you a lot of money, especially the bigger and more expensive your driver is. For around $15 and a little time I was able to repair my driver and salvage my expensive subwoofer.

Doing repair on your speaker may be intimidating to those that aren't experienced with such things, but it is very easy. Let's face it; this isn't rocket science and you don't have to do anything electronic. If you've ever glued popsicle sticks onto construction paper in kindergarten then you're more than qualified to re-edge your speakers (but you may need help with the Safety Scissors).