Recommendations

Death Note
From the Red Fog
Brutal: Satsujin Kansatsukan no Kokuhaku
Mr. Villain's Day Off (this one is more light-hearted)

If you're ok with anime, I'd highly recommend Aoi Bungaku Series. It's a collections of stories made into anime form and from what I remember, most or all of the mc's are not good people (can't remember for sure if there was any harem, but I'm pretty sure there wasn't).