how to transpose a dataframe

I want to transpose a dataframe like
      level   2006   2007   2008
        A       ....
        B      .....
        C        ........
into
      level    year
        A      2006    
        A      2007    
        A      2008
        B      2006
        B      2007
           ......
There is a procedure in SAS can do this, is there any function in R can do this?