I think you have a few options if you want to try to move some players for a starting pitcher...
You can either package a lesser offensive player at a deep position (such as outfield) with Greinke/Haren and go get a true ace like Kershaw or Halladay if possible.
The other option, and in my opinion the more intriguing one, is to sell high on David Freese. I know he's coming off the red hot post season and has had a ridiculous start to 2012, but it is for that exact reason that you may be able to get insane value for him right now from another owner in your league. I wold not dump him by any means, I would try to use him as a key piece to go get another tier 2 starting pitcher (much like a Greinke or Haren) and then you would have three of those tier 2 pitchers on your staff, which would make your overall team much more well rounded and extremely tough to compete with. I think that your offense is good enough to sustain a loss to Freese and that adding another very solid starter could really put your team over the top.
Having trouble getting opinions on my team:viewtopic.php?t=443693