With Pedroia open to shifting to shortstop, the Red Sox now have a lot more options to fill the hole at middle infield. The player that is most discussed has been Marco Scutaro. Scutaro easily had the best year of his career last year, posting a .282/.379/.409 while playing above average defense at shortstop. A long time utility player finally making good on his opportunity to start is a good story, but everything about him seems to point to a disastrous free agent signing. We're talking about a 33 year old player who just posted a career high in slugging and on base percentage, but have never cracked an .800 OPS. We're also talking about a player who walked as much as Kevin Youkilis last year, despite not having any power to speak of. Rob Neyer argues that Scutaro has shown potential to be this kind of player in the minor leagues, but I am unconvinced. I think his 2600 at bats in the major leagues are much more informative than looking back on two seasons of minor league numbers that are now 10 years old. The cherry on top is that Scutaro is also a Type A free agent, so he would cost the Red Sox their first round pick. That is mitigated if they sign more than one type A free agent (Holliday? Lackey?), but giving up much of anything for a glorified utility player would be a terrible blunder.
One option at second base would be Placido Polanco. In a lot of ways he is similar to Scutaro. He hits for a solid average, draws a few walks (although not as many as Scutaro did last year), and hits for a tiny bit of power. The difference between Polanco and Scutaro is that because Scutaro plays shortstop his price will be inflated substantially, and Polanco was not offered arbitration by the Tigers, so he would not cost a draft pick. While Polanco might be an all right stop gap measure, I am not sure that he would improve the Red Sox very much.
Edit: Polanco has signed with the Phillies for 3 years and $18 million to play third base. His bat is a little bit light to play there, although he should still be an upgrade over Pedro Feliz. Plus, with Utley, Rollins, and Howard in that infield they can handle a bit less than average production from third.
I think the most attractive option at second base is Orlando Hudson. Hudson is two years younger than Scutaro and could be relatively cheap coming off a "down" year in Los Angeles, where Torre benched him down the stretch and in the playoffs in favor of Ronnie Belliard. Despite having his worst offensive year of the last four, Hudson still put up a .774 OPS, just slightly worse than Scutaro's career year. Hudson would also benefit from Fenway, turning five to seven fly outs into doubles or home runs. Because he isn't a home run hitter, the triangle in right center would not harm him either. Assuming the Red Sox aren't able to pick up a middle infielder through a trade, Hudson seems like the obvious, and cheaper, option to me.