These two are the best around. Lookout Landing has high standards generally so read a bit before posting. USS Mariner generally has good articles especially with Jeff Sullivan writing there occasionally.
If you are into prospects/trade rumors ProspectInsider.com has a lot of Mariners content.
The people on lookout landing are super annoying to people with differing opinions and they all seem to have a hard-on for the same type of off-beat humor that I cant entirely describe. As you can tell Im not a fan but they have some decent content