There are quite a few big name signings, that really won't change the free agent's value much, but it could improve the performance of his new teammates.
The most obvious player to benefit from joining a new team will be Barry Zito's move to the NL. A top American League starting pitcher moving to the National looks like an obvious choice for fantasy owners looking to get a lot of upside from a pitcher that they can draft in rounds 9 through 12; however, I think you may get even more value from a hitter like Aubrey Huff.
Huff will likely be drafted after round 15 in most fantasy baseball drafts, but if he regains the form he had in 2003 and 2004, he could produce numbers worthy of a fifth round draft pick. Huff will likely benefit from having a certain future and being in a great hitters park where he has a good career batting average.