An analysis by Avalere Health found that seven of the top 10 Medicare Prescription Drug Program (Part D) plans will increase their premiums 3 to 43 percent in 2011.  The other three plans will lower their premiums 2 to 11 percent over the same period. 

From the article:

Avalere Health LLC released further analysis of the Centers for Medicare and Medicaid Services (CMS) Medicare Part D landscape file for 2011 showing that the weighted average monthly premiums for the top 10 prescription drug plans (PDPs) will increase by 10 percent in 2011. These plans cover approximately 70 percent of Medicare PDP enrollees. 

Full Article: Premiums for the Top 10 Medicare Prescription Drug Plans Will Rise by an Average of 10% in 2011 (HTML)   

Avalere Health. (2010). Premiums for the top 10 Medicare prescription drug plans will rise by an average of 10% in 2011. Martin, A.