I've added a links section to my page, with the following awesome sites:
MLB Trade Rumors--I check this page several times a day. It gathers all the latest rumors and announcements on trades, free agent signings, roster moves, and the like. It also provides links to the many articles it cites and gives well-informed feedback, judging the seriousness of each rumor and the implications behind a move. E.g. The Crede signing and early talk of a midseason Halladay trade.
Baseball-reference.com--This is an amazing site giving career statistics for players past and present. You can also link into the minor league section, which will give you minor league stats since they became readily available. I'll often check here to see how much time a given player has spent at each position in their major and minor league years. E.g. Mark Teahen, 256 games at 3B, 229 at RF, 31 at LF, 23 at 1B, 6 at CF, and 1 at DH, in the Majors. In the minors, exclusively 3B, at least since the high-A Modesto A's. Some minor league data is incomplete, usually rookie and short-season leagues.
FanGraphs.com--Another stat site, Fangraphs gives you a lot of advanced sabermetric stats for free. You can see BB%, K%, LD%, FB%, GB%, HR/FB, wOBA, BABIP, WPA/LI, splits for pitch type, fielding value, career graphs, and their projection of an appropriate contract value. They also provide a convenient one-stop look at the Marcel, CHONE, Oliver, and Bill James projections. E.g. Shin-Soo Choo is projected by Marcel at a .373 wOBA, by CHONE at .354, by Oliver at .347, and by Bill James at .359. Average those out for .358.
MLB Depth Charts--A new discovery brought to my attention by MLB Trade Rumors, they've given a run-down of each team's likely roster set-up and depth chart, with a little commentary and a long list of who might make the team. E.g. They've already updated Joe Crede into the 3B slot, describing him thus: "hit .252 with 16 HR's and 49 RBI's in the first half of the season as he was named to his first all-star team but he only batted 39 times the rest of the way because of a back injury." They do seem to rely on AVG a lot in their descriptions, but just in a quick here's-what-the-guy-looked-like kind of way.
Inside The Book--run by Tom Tango and the crew who wrote The Book: Playing the Percentages in Baseball, there is a lot of wonderfully statistic sabermetric discussion here. Look in the comments under the headings of their blog, and you will find numbers-based discussions of what's happening in the baseball world. E.g. They've had plenty of discussion on the 'true value' of the free agents on this year's market.
Hardball Times--another fun site of sabermetric analysis. I've read several articles here recently utilizing the PITCHf/x data and starting to draw analytical conclusions from the data. E.g. Hitters have trouble hitting the low-outside fastball at any speed, but are consistently better at nailing the middle-in fastball the slower it goes. Based on math now, not intuition.
I'll probably add to the sites in the future; these are just the ones I thought of now. I've been frequenting them, as I build my perceptions about the coming season and beyond.
Speaking of which, I've been waffling, and I'm not as sold on the Twins as I was earlier, though Crede bumps them back up. I'm starting to slot Chicago into #2 in the AL Central. And while I might bump the Yankees up to #2 in the East over the Rays, it's quite close. I love Boston's depth, and I think they're still the team to beat, not only in the AL East, but probably in the Majors.