since you asked for "left leaning" and you are looking to have sources from all "sides", you should check out the New Republic and Mother Jones, in addition to

since you asked for "left leaning" and you are looking to have sources from all "sides", you should check out the New Republic and Mother Jones, in addition to mostly middle of the road picks like Washington Post (edit: yes and also The Guardian as someone else mentioned). I also highly recommend Talking Points Memo. Clearly not the HN user's cup of tea but that's what we libs are reading.