Let us use the same idea as the previous example and assume we want at least one employee from every department. The only requirement for the following query is that you are asking for more employees than you have departments.
select top 100 T1.* from
(PARTITION by Department order by newid()) as r,
where Active = 1
) as T1
order by t1.r, t1.Department
Note, as before, that this is a sql server query. Modifications may need to be made for different flavors of SQL. What this is doing is for every department the employees are getting randomly ranked thanks to order by NEWID(). By selecting the top 100 and ordering by rank and then department, you'll get all of the 1's from every department, then all of the 2's and so on until you get 100.
The order by department is strictly unnecessary. I did it to make viewing and verifying the results easier.