The official blog from Xojo Inc.
The official Xojo Blog
Bob has for long time had blog on Xojo development.
I really like this one (probably since I tend to agree with Bob on many things)
MBS Plugin Blog – He is supposed to be competitor but the Xojo community is small and it is hard to see anyone as competitor in a small community where people know each other. (I met Christian in Reykjavik 2015, making him the 3rd from the Xojo community that I meet with in person)