Traditionally, a DJ's mixer has been the nerve center of his rig, and its power and flexibility has grown over the years as DJ culture has moved more and more to the forefront of the music scene. We've come a long way from the early days of mixers cobbled together from what you could find a your local electronics store, that were basically nothing but two faders for the left and right turntables and, if you were lucky, a crossfader for quick cuts. Modern DJ mixers have added massive amounts of EQ, heavy-duty DSP for a huge bank of FX, even software control that ties into packages like Traktor or Serato. So what used to be a simple choice has gotten much more complex.
DJ mixers can be mostly broken down into two categories: scratch (or battle) mixers, aimed at DJs with serious turntable skills who practice techniques like scratching, beat juggling and drumming and club mixers aimed at DJs who work more with segues, beat-matching and harmonic mixing. Many modern mixers also have built-in loop sampling and triggering for doing live, on-the-fly remixing.