Social Security recently announced that you can use your online account to get a replacement Medicare card if your card is lost or damaged. You can also get statements from Social Security regarding your earnings, and estimate regarding future benefits.
Among other things you can do, you can get a letter with proof of your benefits. You can manage your account, change your address, start or change your direct deposit, and get a replacement SSA-1099 or SSA-1042S for your taxes.
You can set up or access an account at: http://www.socialsecurity.gov/myaccount/