Who to keep and who to throw back are amongst the toughest decisions fantasy players face each spring. This is especially dificult in long-running AL-/NL-only keeper leagues. With half the player pool and the same number of roster spots as mixed leagues, every team knows there are price distortions for available players.
This is not a clear-cut decision as those distorted prices make for large disagreements. (See the discussion on $17 Nick Markakis for a $24 Magglio Ordonez and $1 Nick Punto.)
With that said, this is from Tristan Cockcroft's chat on ESPN:
Tristan H. Cockcroft: (11:41 AM ET ) First of all, I'd keep Johan Santana. He's easily a $50 player in AL-only formats. I'd also retain Felix Hernandez at that price. Among the hitters, I'd call Craig Monroe and Gary Matthews Jr. reasonable bargains at those prices. Let the rest go, as you should be able to get them back at no more than those prices.
Assuming a $260 AL-only format, I think all of those players are protectable except Jesse Crain. Did Mr. Cockcroft miss the "AL only" condition? (And a $46 Johann Santana is far from a sure thing to keep!)