Alex Gordon is better than people think. He's yet to reach superstar status, but Gordon's two seasons have been above average. Obviously you would hope for a little more, considering his draft status, but look as his numbers. Gordon saw his walk rate and ISO increase, and if he can play defense more like 2007 and less like 2008 while continuing to hit, he could easily be worth ~3.5 wins, if not more.
Gil Meche has been worth his contract thus far. I didn't like the deal at the time, but Meche has been surprisingly good over the last two seasons thanks to improved walk and homerun allowed numbers.
Jose Guillen. Ugh. I never liked that deal.