mendixandbeyond of course :)
I have most blogs I ever found on Mendix bookmarked so I check them every once in a while. Here's my list:
These have been updated lately:
Older blogs, most of them not updated in the last 6 months:
Anyone else want to share which blogs they frequent?
http://bartgroot.nl/ but it hasn't been updated in a while. Otherwise I live off StackOverflow, not a blog but useful for general development.