Burnout Paradise

Easy way to so this - Find Chubb lane and go there, and there is 3 parked buses at one end of the street, go into showtime and get them, keep traveling down the street in showtime and you'll come accross many more buses in this street. (when i got this achievement I got to 13X multiplyer :) )

Real easy achievement, all you have to do is to smash 10 buses to gain a 10X multiplier. As Mile AU wrote Chubb Lane is a good place to start, Although it if you're not close when you decide to get the achievement it takes longer to drive to Chubb than to find three buses.

Try to stay to larger streets, as they holds the most traffic. Good luck!

If you're not familiar with Showtime, it's entered by pressing LB+RB while free roaming. This will make your car "crash," and you can then control it as it flips and careens through traffic. Hitting A will consume some of your boost meter and bounce you off the ground so you can keep your momentum going. Each vehicle you hit will increase your score and fill your boost. If you come to a stop on the ground, your boost will quickly drain, and if you're stopped with no boost left, Showtime is over.

The only way to increase your multiplier is to hit buses. The main strategy here is to conserve your boost as much as possible, because depending on your luck with vehicle spawning, it may take a while to find ten buses. If there are no buses around, rely on your momentum as much as possible and minimize use of boost.

The other guides recommend Chubb Lane. Webster Avenue is also a good place to work on this achievement. On the section just north of the parking garage, there are usually two buses parked, and buses regularly spawn along Webster and along nearby 7th Street.