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The "typical v8 roar" really depends on the sensitivity of your ears. Exhaust tuning (muffler/resonator placement, piping size, h/x pipes, cats, etc) can change the sound drastically, so you should figure out what type of sound you're going for.
I think nearly all JDM or jdm inspired exhaust systems have mufflers with a straight through design. Other brands of straight through mufflers include Borla and Magnaflow. The other choice you have is a chambered muffler, this is the style that Flowmaster is known best for.
Look through the extensive exhaust thread on clublexus as well as youtube for all the different exhaust setups. I haven't heard an IS-F clearly in real life yet (I'm sure I'm missing out), but if you want to make it just slightly louder, an axle back will probably be your best bet.