This has always been quite the question here, use the search bar and I'm sure you'll find someone else having asked the same thing and several (different) answers. Some, like SnootyEnglishman up here, suggest an air compressor, but some say it could potentially loosen some of the PS3 parts and thus don't reccomend it. Some say a vacuum, but as you experienced, it doesn't get EVERYTHING out.
My reccomendation would be to get one of those compressed air cans for microprocessors and blow the air out as much as you can. Of course, someone will point out that it doesn't really get rid of the dirt but rather it reaccomodates it inside the PS3, which could very well be true.
So, the solution? Damn if I know. I'm still waiting for a definitive answer myself...