You can use some domain names generators such as namemesh (already suggested by joniboini), namestall, domainnamesoup... all you have to do is to provide some keywords and they will generate free related domain names. At least they will give you some cool ideas.
But keep in mind that your website popularity doesn't depend on it's url but on the content you provide and a cool name won't improve your ranking on search engines. So don't waste too much time on it.