Y'know. Stuff you listen to at night, as opposed to during the day.
I find myself listening to a lot of post rock, fairly obviously. Anything with plenty of fx and build up and delicacy. Mono, MBV and Mogwai especially.
I also find myself listening to a lot of 'driving' stuff. With a real pulse, and a rolling beat, but simultaneously kinda 'close your eyes and drift away'. Like right now, I've just whacked on None Shall Pass by Aesop Rock. I find the laidback flow fits really well to working late at night or reading, or just generally kicking back. In fact a lot of stuff with beats as opposed to guitars are welcome in the twilight zone.
What do you find yourself listening to? Is it significantly different to your daytime listening habits?