String "Aggregates" Solution

Even though I promised to update a solution to a problem,  I failed to do so for a long time.

Here is the problem

If you need to get the sum of salary by department we may be able to use Sum and group by clauses in a single select statement to get it done.  But if you have a situation where you need to give a comma separated string of employees for each department, how will you handle it?
Consider these tables:

Department Table

DepartmentID	DepartmentName
1	Sales
2	IT
3	Finance

Employee Table

EmployeeID	DepartmentID	EmployeeName
1	1	Sales Person 1
2	1	Sales Person 2
3	2	Developer 1
4	2	Developer 2
5	2	DBA 1

Now you want the results like this:

DepartmentName	EmployeeList
Sales	Sales Person 1, Sales Person 2
IT	Developer 1, Developer 2, DBA
Finance	NULL

Here is the code for yesterday's Scenario:
create table #Department
(
DepartmentID int not null primary key clustered,
DepartmentName varchar(10) not null
)

create table #Employee
(
EmployeeID int not null identity primary key clustered,
DepartmentID int,
EmployeeName varchar(100)
)


insert #Department values(1, 'Sales'), (2, 'IT'), (3, 'Finance')
insert #Employee values (1, 'Sales Person1'), (1, 'Sales Person 2'), (2, 'Developer 1'), (2, 'Developer 2'),(2, 'DBA')

How to "aggregate" on strings

If you need to get the sum of salary by department we may be able to use Sum and group by clauses in a single select statement to get it done. But if you have a situation where you need to give a comma separated string of employees for each department, how will you handle it?
Consider these tables:

Department Table

DepartmentID	DepartmentName
1	Sales
2	IT
3	Finance

Employee Table

EmployeeID	DepartmentID	EmployeeName
1	1	Sales Person 1
2	1	Sales Person 2
3	2	Developer 1
4	2	Developer 2
5	2	DBA 1

Now you want the results like this:

DepartmentName	EmployeeList
Sales	Sales Person 1, Sales Person 2
IT	Developer 1, Developer 2, DBA
Finance	NULL