Crossposted from Primer:
Advanced NFL Stats - More of a look at the game theory of football than a Football Outsidersesque stat site.
Cardboard Gods - Josh Wilker's unique brand of nostalgia. Might be some existentialism involved as well (I was never good at philosophy.)
Driveline Mechanics - Batting and pitching mechanics
Evaluating Baseball Managers - Chris Jaffe's publicity site.
Fangraphs - The WSJ of the sabersphere. They're pretty good at getting transaction news out and other info out, but you'll either love or hate the editorials.
Free Darko - An offbeat take on the NBA.
Joe Posnanski - This one needs no publicity.
Prolate Spheroid - college football history.
Residual Prolixity - Posts from a Tennessee Titans fan that don't fit his other venues. Only place I know that reviews old books about football.
Sabermetric Research - Phil Birnbaum's frustration with academics who try to do econometric research about sports without understanding the sports they are researching.
Smart Football - Like Advanced NFL Stats only for the NCAA. Also shows a lot of charts and video of plays. Loves the spread offense.
The Book Blog - Tango and MGL's hangout.
Walk Like A Sabermetrician - Occasional posts from Patriot; an Ohio based guy.
That's all the sports ones. I really don't follow the blogosphere for much else; except the funny pages.