Last Podcast On The Left is my favourite, although it's not for everyone. They cover the occult and conspiracy theories, too.
Generation Why is very thorough. I also like Casefile.
There's a BBC Radio 4 series called Who Killed Elsie Frost which is good.
There's also Someone Knows Something. The first series was the best one and there are ongoing updates. The most recent one was good but the sound editing was appalling and I almost stopped listening due to all the wet sniffling (if you've listened you'll know what I mean!). CBC Radio has a few about Native Canadians that are really good.
I tried My Favourite Murder but their utter lack of knowledge and inane chat got on my nerves.
I recently listened to a spoof crime podcast called Done Disappeared, it's hilarious! The takes on all the popular crime podcasts are spot on and recognisable. But you have to have listened to a few different to really get the humour and references. Worth a listen if you have.