I always read Matt Cutt's blog, just because once in a while, he'll let something slip that has been pure conjecture in the past. Unfortunately, I've lost a lot of confidence in his reliability over the last year or so.
I like Rand Fishkin http://seomoz.org/blog
a lot, for the same reasons as Guy. He's not afraid to call a spade a spade, and I find he's usually right. Him, I trust to be honest, and he's well informed enough to be reliable, nine times out of ten.
Another blog I like is John Britsios (Webnauts). His blog is almost more like a newsletter, but John really keeps his ear to the ground, and is more often right than wrong. He can be opinionated, but then, can't we all? And I find that being opinionated is more forgiveable when a guy knows what he's talking about. You can check him out at http://blog.webnauts.net/