How to pivot two columns in SQL Server?

I have the following table

 UserName   UserId   
    -----      ----    
    Bob         445       
    Bob         450       
    Rachel      512       
    Rachel      520       
    Rachel      570       
    Simon       771       
    Simon       760 

and I am trying to pivot it so that a new column is created for each username, with UserID’s listed per UserName

Bob       Rachel       Simon
445          512        771
450          520        760
             570

Answer

Just in case you were looking for a dynamic pivot

Example

Declare @SQL varchar(max) = '
Select *
From (
        Select * 
              ,RN = row_number() over (partition by username order by UserId) 
        from #YourTable
     ) A
 Pivot (max(UserID) For [UserName] in (' + stuff((Select distinct ',' + QuoteName([UserName]) From  #YourTable Order By 1 For XML Path('')),1,1,'')  + ') ) p
'

--Print @SQL
Exec(@SQL);

Returns

RN  Bob   Rachel    Simon
1   445   512       760
2   450   520       771
3   NULL  570       NULL