It's kinda hard to rate teams like RSNT, OPQS etc., so leaving them out I think the most improved teams are:
1) BMC: Hushovd, Gilbert, TJVG, Pinotti are all great additions to a team lacking depth and Lodewyck, Blythe and Cummings are all very good riders as well.
2) Movistar: Visconti, Moreno, Herrada, Castroviejo will all do well, and Quintana is one of the biggest talents around. Add to that the returning Valverde...
3) Astana: Brajkovic, Ponzi, Gavazzi are all big names, and add Seeldraeyers, Bozic, Guarnieri and Silin and the team is looking very well rounded.
It's still early to tell though as a lot more can and will happen on the transfer market, and if Cavendish moves to Sky they'll be up there as well.