Now one of the main factors here will be whether you need the ground of your 12V supply to be the ground of your circuit - in other words, can/is the 12V supply floating? If so, Generating a middle point as "virtual" ground may be the easiest. It can be buffered with an adequate opamp for instance (one that can source and sink enough current.)
If cost is not a factor, there is a pretty nice all-in-one solution with the LTC3260 (wide input range, integrated inverting charge pump, integrated post-reg LDOs). It's rather expensive though.