John Baez rocks. In general. All of his stuff is great and his writing style will cheer you up when you feel like you need to go back to freshman calculus.
I read some of his pieces on Lie algebras and A-D-E classifications. Very helpful.
Baez is awesome. I used to follow his news-in-mathematical-physics digests back in the 90ies (basically a blog years before there were blogs); sadly almost everything went over my head. I dream of finding time and stamina to study enough background material to understand his Rosetta stone paper well.
I read some of his pieces on Lie algebras and A-D-E classifications. Very helpful.