Most of all they need a center fielder. Teheran most definitely is a #1 starter and leads one of the best rotations in baseball. The problem is the Uggla and BJ Upton deals are killing their financial flexibility and the prospect list is bare.
The good news is that the core is very young, under long term contracts, and very good (Simmons, Freeman, Teheran, and Heyward). They should be able to build around this group. But they need a true leadoff hitter in a major way, preferably a center fielder.