Buy Low
Ryan Howard - Assuming you aren't deluding yourself into Howard being a .280-.290 hitter, now is a good time to inquire about the big power bat.
David Ortiz - Ortiz is showing signs of life and it would be hard to believe he has fallen this far off a cliff. It's just a slump.
Justin Verlander - Just got dropped in my league and I happily picked him up. His WHIP is reasonable, though the strike outs are down. He should eventually put things together and dominate.
Chad Billingsley - His 5.20 ERA is masking his phenomenal 40 K's in 27 2/3rds innings. Look for the ERA and WHIP to continually shrink as the season wears on, while Billingsley continues to rack up K's.
Robinson Cano - Cano isn't really striking out that much, so it leads me to believe that he's having bad luck with balls he makes contact with. This, after two straight years of flukishly above average luck with balls in play. Expect him to settle into being a .280-.290 hitter. (Cano actually sits on the waiver wire in my league but I can't pick him up because I have some kid named Chase Utley in my 2B slot.)
Sell High
Chipper Jones - Chipper, or Larry as his mom calls him, can rake. And he is raking. His numbers will come down, but they will still be good. However, Larry struggles to stay healthy and with no DH to buy some rest, will eventually see some time on the DL. Now would be a good time to quietly shop him around to see what you can get.
Troy Percival - Injury prone closer. For the Devil Rays. Make sure you point out his 0.00 ERA to trade partners.
Fausto Carmona - He had a big season last year and a reasonable start to this season but there are lots of things indicating a big time implosion is on the way. First off, he doesn't strike many batters out and he's giving up way more hits and walks than suggested by his ERA.
Albert Pujols - This depends on how bad you think his injury is and how good you think the Cardinals are. My thinking is the Cards will be out of contention in a few months and Pujols may elect to get surgery out of the way early to prepare for next year. Sell while he's still healthy.
Cliff Lee - Obviously. He's nowhere near this good.
Hold Steady
Carlos Beltran - Not much you can do if you own him. Numbers aren't good to start the season, meaning you can't really trade him, though with his injury concerns I wouldn't want to trade too much for him, either.
Travis Hafner - Spronk doesn't look good up there right now. At this point all you can do is hold on and hope he gets his swing back.
Tim Lincecum - He's 100% legit and may still get 13-14 wins in spite of his teammates.
C.C. Sabathia - You can't trade for him because he still has too much (perhaps undeserved) name recognition. And you can't trade him if you own him because you invested too high a pick and won't get enough return.
