Most typically in SQL Server I see this technique used:

SELECT TOP ...
FROM dbo.table_name
ORDER BY NEWID()

I presume that gives a roughly random sample.  Of course it likely does require sorting the entire record set.

If you have an existing index that contains a unique set of columns, you could select just those columns in the "ORDER BY" query, allowing an index scan and sort rather than a full table scan and sort, then join back to the main table after that to get other column(s) from the table.